Method and apparatus for handling communications between spacecraft operating in an orbital environment and terrestrial telecommunications devices that use terrestrial base station communications

ABSTRACT

A multiple-access transceiver handles communications with mobile stations in environments that exceed mobile station design assumptions without necessarily requiring modifications to the mobile stations. One such environment is in Earth orbit. The multiple-access transceiver is adapted to close communications with mobile stations while exceeding mobile station design assumptions, such as greater distance, greater relative motion and/or other conditions commonly found where functionality of a terrestrial transceiver is to be performed by an orbital transceiver. The orbital transceiver might include a data parser that parses a frame data structure, a signal timing module that adjusts timing based on orbit to terrestrial propagation delays, frequency shifters and a programmable radio capable of communicating from the Earth orbit that uses a multiple-access protocol such that the communication is compatible with, or appears to the terrestrial mobile station to be, communication between a terrestrial cellular base station and the terrestrial mobile station.

CROSS-REFERENCES TO PRIORITY AND RELATED APPLICATIONS

This application claims priority from and is a Continuation of U.S.Non-Provisional application Ser. No. 15/916,909, filed on Mar. 9, 2018,entitled “Method and Apparatus for Handling Communications BetweenSpacecraft Operating In An Orbital Environment and TerrestrialTelecommunications Devices That Use Terrestrial Base StationCommunications” which is a Continuation-In-Part of U.S. Non-Provisionalapplication Ser. No. 15/857,073, filed on Dec. 28, 2017, entitled“Method and Apparatus for Handling Communications Between SpacecraftOperating In An Orbital Environment and Terrestrial TelecommunicationsDevices That Use Terrestrial Base Station Communications,” which claimsthe benefit of U.S. Provisional Patent Application No. 62/490,298 filedApr. 26, 2017 entitled “Method for Communications Between Base StationsOperating in an Orbital Environment and Ground-Based TelecommunicationsDevices.”

This application also claims the benefit of U.S. Provisional PatentApplication No. 62/465,945, filed Mar. 2, 2017 entitled “Method forLow-Cost and Low-Complexity Inter-Satellite Link Communications within aSatellite Constellation Network for Near Real-Time, Continuous, andGlobal Connectivity” and claims priority to U.S. patent application Ser.No. 15/910,959, filed Mar. 2, 2018, entitled “Simplified Inter-SatelliteLink Communications Using Orbital Plane Crossing to OptimizeInter-Satellite Data Transfers.”

The entire disclosures of applications recited above are herebyincorporated by reference, as if set forth in full in this document, forall purposes.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for handlingcommunications between spacecraft and terrestrial telecommunicationsdevices, more particularly to communications using features andfacilities of the terrestrial telecommunications devices that aretypically used for terrestrial telecommunications.

BACKGROUND

Mobile communication involves signals being sent between a mobilestation (MS) and a transceiver that can provide an interface for the MSto communicate to and from other network resources, such astelecommunication networks, the Internet, and the like, to carry voiceand data communications, possibly also location-finding features. Thetransceiver might be a component in a base transceiver station (BTS)that handles traffic from multiple transceivers. The BTS might alsoinclude antennas and encryption/decryption elements. The antennas mightbe selective antennas, wherein different MSs at different locationsmight communicate to their respective transceivers via differentantennas of the BTS. The BTS may have a wired, wireless, and/or opticalchannel to communicate with those other network resources. A BTS mightsupport one or more transceivers and a given base station for supportingmobile communication might have a base station controller (BSC) thatcontrols one or more BTS of that base station.

Examples of mobile stations include mobile phones, cellular phones,smartphones, and other devices equipped to communicate with a particularBTS. While herein the mobile stations are referred to by that name, itshould be understood that an operation, function or characteristic of amobile station might also be that of a station that is effectively orfunctionally a mobile station, but is not at present mobile. In someexamples, the mobile station might be considered instead a portablestation that can be moved from place to place but in operation isstationary, such as a laptop computer with several connected peripheralsand having a cellular connection, or the mobile station might bestationary, such as a cellular device that is embedded in a mounted homesecurity system. All that is required is that the mobile station be ableto, or be configured to, communicate using a mobile communicationinfrastructure.

A BTS might be controlled by a parent BSC via a base station controlfunction (BCF). Each of these elements could be implemented usinghardware and/or software and include network management and maintenancefunctionality, but a base station can be described as having one or moretransceiver that communicate with mobile stations according to anagreed-upon protocol. This can be by having the BTS being configured,adapted or programmed to operate according to the agreed-upon protocolfor a BTS and having the MS being configured, adapted or programmed tooperate according to the agreed-upon protocol for a MS. The protocolmight include details of how to send data between a transceiver and aMS, how to handle errors, how to handle encryption, and how to sendcontrol instructions and status data between the BTS and the MSs. Forexample, parts of the protocol might include interactions wherein an MScontacts a BTS and the BTS indicates to the MS what timing, carrierfrequency, and other protocol options the MS is to use. This interactionmight include carrying voice data, carrying text data, carrying otherdata, providing for intracell handover and other tasks.

For simplicity of explanation, in many examples herein, communicationsis described as being between a BTS and a MS for interactions with oneMS, but it should be understood that the interactions might be from aBTS to a transceiver, to a radio circuit, to an antenna, to a MSantenna, an MS radio circuit, to software/hardware in the MS, and acorresponding path in the other direction from the MS to the BTS. Thus,in some examples where a BTS is communicating with an MS, it is via atransceiver and the example ignores mention of the other transceiversthat the BTS might be controlling.

Examples of protocols that a BTS might use includes GSM (Global Systemfor Mobile Communications; trademarked by the GSM Association) 2G+protocols with Gaussian minimum-shift keying (GMSK), EDGE protocols withGMSK and 8-PSK keying. A BTS might handle multiple transceivers that usemultiple sets of carrier frequencies within a spectrum band of wirelessspectrum that the protocol allows for. Thus, where a spectrum band islogically divided into carrier frequency spectra, a transceiver mightuse channels that use one (or more) of those carrier frequencies tocommunicate with an MS. The protocol might specify that for a givenchannel, there is an uplink subchannel and a downlink subchannel,possibly separated in carrier frequency from each other. In some cases,the uplink subchannel has a carrier frequency adjacent to that of thedownlink subchannel. In some cases, all the uplink subchannels are inone spectrum band and all the downlink subchannels are in anotherspectrum band. For ease of explanation, sometimes a channel is describedas having an uplink portion and a downlink portion as if it were onechannel, even if the portions are widely separated in carrier frequency.

Some BTSs might provide for frequency hopping, where the transceiversand the mobile stations rapidly jump together from carrier frequency tocarrier frequency to improve overall BTS performance. The protocol mightspecify the hopping sequences to use.

In the GSM protocol, transceiver-MS communication involves frames andeach frame has up to eight timeslots. With eight timeslots, atransceiver sends out a frame that is directed at up to eight MSs, witheach MS assigned a unique timeslot in the frame by the transceiver'sBTS. The MSs can send their transmissions in their allotted timeslot andsince each MS that is communicating with that transceiver knows whichtimeslot they are to use, similarly situated MSs can communicate back tothe transceiver in their allotted timeslot. A transceiver might not useall eight timeslots.

A signaling channel, such as the GSM protocol's Common Control Channel(CCCH) might be used to convey to the MSs what their allocations are fortimeslots and carrier frequencies. For example, some Common ControlChannels are used to make access requests (e.g., making RACH requests,which are from a MS to a BTS), for paging (e.g., making PCH requests,which are from a BTS to a MS), for access grant (e.g., an AGCH, which isfrom a BTS to a MS), and cell broadcast (e.g., CBCH, which is from a BTSto a MS). The AGCH (Access Grant Channel) is used for granting timeslotallocations/carrier allocations. Another channel, the Broadcast ControlChannel (BCCH) might or might not be used to send information to the MS,such as Location Area Identity (LAI), a list of neighboring cells thatshould be monitored by the MS, a list of frequencies used in the cell,cell identity, power control indicator, whether DTX is permitted, andaccess control (i.e., emergency calls, call barring, etc.).

Examples of BTSs include cellular telephone towers, macro-celltransceivers, femto-cell transceivers, picocells (which might have onlyone transceiver) and the like. BTSs will communicate with MSswirelessly. Some BTSs have a backhaul (the interface between the BTS andthe other network resources) that is wired, such as with a cellulartelephone tower, while some might have a wireless backhaul, such as amicrowave point-to-point bidirectional communications channel. Thus, aBTS might be any of several different types of electrically powereddevices that receives data streams from MSs and processes those and/orforwards them to other network resources, as well as receiving datastreams from the other network resources and processing those and/orforwarding them to MSs over the BTS-MS link(s). In this sense, a BTSacts as an access point for the MSs, to allow an MS to access networkresources such as a telecommunications network, the Internet, privatenetworks, etc. The access might be used to route voice calls, othercalls, texting, data transfer, video, etc.

A telecommunications network behind a BTS might include a network andswitching subsystem that determines how to route data to an appropriateBTS and how to route data received from a BTS. The telecommunicationsnetwork might also have infrastructure to handle circuit connections andpacket-based Internet connections, as well as network maintenancesupport. In any case, the BTS might be configured to use some protocolswith MSs and other protocols with the backhaul.

The protocols for communication between MSs and BTSs might be such thatthey are standardized so that any standard MS can communicate with anyBTS, assuming range requirements are met and membership requirements aremet (e.g., that the MS has identified itself to the BTS in such a mannerthat the BTS, or a service that the BTS uses, determines that the MS isa member of an authorized group or otherwise authorized to use theservices provided by the BTS. Some example protocols include the GSMprotocols, sometimes referred to as 2G (i.e., second generation) networkprotocols. Other examples include GPRS (General Packet Radio Services),EDGE (Enhanced Data rates for GSM Evolution, or EGPRS), 3G(third-generation 3G UMTS standards developed by the 3GPP body, orfourth-generation (4G) LTE Advanced protocols.

In these protocols, there are rules for spectrum band use, timing,encoding and conflict resolution. As a BTS is likely to have tocommunicate with many MSs at the same time, the available wirelesscommunication pathway is divided up according to the protocol. A givenprotocol might have the available wireless communication pathway dividedup by frequency, time, code or more than one of those. This allowsmultiple users to share the same wireless communication pathway.

For example, with a Time Division Multiple Access (TDMA), the BTS andthe multiple MSs agree on the division of time periods into timeslots(or “burst periods”) and where a first MS might interfere with a secondMS, the first MS is assigned a first timeslot and the second MS isassigned a different timeslot of the available timeslots. Sincedifferent MSs use different timeslots (and they all agree on timingsufficiently well), they can share a common carrier frequency and theirrespective transmissions do not interfere. An example would be wherethere are eight timeslots of 576.92 μs (microseconds) each for eachframe and so an MS assigned the first timeslot will perhaps transmit anumber of bits during the first timeslot, stop transmitting at or beforethe end of its timeslot, remain silent, then during the first timeslotof the next period, continue transmitting, if desired. Similarallocations occur for a MS to determine when it is to listen forsomething from a BTS (and for the BTS to determine when it is to starttransmitting that data).

Thus, using a single carrier frequency, each transceiver of a BTS cancommunicate with up to eight MSs and communications to those MSs isgrouped into a TDMA frame and transmitted on the downlink channels thatuse that carrier frequency channel. The timing is such that each ofthose MSs can communicate in their respective timeslots to the BTS onthe uplink channels that use that carrier frequency channel. This isreferred to as a “TDMA frame” and the data rate over all eight MSs usingthat carrier frequency is 270.833 kilobits/second (kbit/s), and the TDMAframe duration, in either direction, is 4.615 milliseconds (ms).

Frequency Division Multiple Access (FDMA) is another way to divide upand allocate the available wireless communication pathway. With FDMA,the spectrum bandwidth available or allocated for the wirelesscommunication pathway is divided up into different channels by carrierfrequency. A first MS might be assigned one carrier frequency and asecond MS might be assigned another carrier frequency, so that both cansend or receive to or from one BTS simultaneously.

In the above examples, a plurality of mobile stations communicate with aBTS perhaps simultaneously, wherein communication between the BTS and aspecific MS comprises sending information in a signal from the specificMS or from the BTS such that collisions of wireless signals are avoided,by having the BTS and the specific MS agree on which timeslot of aplurality of timeslots is to be used (TDMA), and/or agree on whichcarrier frequency of a plurality of carrier frequencies is to be used(FDMA). These are examples of multiple-access communications.

In another type of multiple-access communication, called “OrthogonalFrequency Division Multiple Access” (OFDMA), mobile devices are assignedsubsets of subcarriers, where orthogonal narrow frequency subchannelsare assigned to mobile devices for more efficient use of allottedspectrum compared to FDMA.

In some frequency allocations, the allocation is per channel block,where a channel block is a set, or group, of bidirectional channels,wherein each bidirectional channel uses an uplink carrier frequency foran uplink subchannel and a downlink carrier frequency for a downlinksubchannel. The channels might be grouped together into sets of two ormore channels based on some logic for classification such that each setshares a common identifier or attribute.

In some protocols, the spectrum is divided into subspectra for carrierfrequencies and also the periods are divided into timeslots. Typically,the BTS includes logic to determine which channels to allocate to whichMSs. In assigning a channel for use by a MS, the BTS might assign aparticular transceiver to use a particular carrier frequency andindicating to an MS that it is to use that particular carrier frequencyand also indicate which timeslot to use from a frametransmitted/received using that carrier frequency. The channel mightcomprise an uplink subchannel and a downlink subchannel. It may be thata given transceiver-MS communication uses more than one channel, e.g.,more than one carrier frequency and/or more than one timeslot, but inmany examples herein, the protocol is illustrated as being with respectto a MS that uses a channel comprising just one carrier frequency andjust one timeslot.

In yet another example of multiple-access communications, called “CodeDivision Multiple Access” (CDMA), mobile devices might use the sametimeslot and carrier frequency, but each mobile device is assigned aunique pseudorandom code to encode the signals to and from the BTS suchthat even when MSs simultaneously transmit using the same carrierfrequency, or almost the same time, and/or the same timeslots, if thoseare used, applying the unique CMDA code allows for multiple transmittersto occupy the same time and frequency, as the receivers can separate outdifferent receptions by decoding using the pseudorandom codes to decodeeach specific signal well enough for demodulation.

In effect, CDMA separates the channels not strictly by time or strictlyby frequency. The use of CDMA results in a transmission ofspread-spectrum signals, spread across a larger bandwidth than withoutencoding, by using a chipping rate that is faster than the signal bitrate. Thus, encoding signals with pseudorandom codes can replace thetiming and frequency elements typically found in TDMA/FDMA protocols, aseach code represents some element of articulation in both the time andfrequency domain. In CDMA communications, signal propagation delay andtiming between the MS and the BTS is understood and so the pseudo-randomcode is applied to a received signal across some number of bits/chipswhich, of course, occupy both some discretized span of the time domainand some discretized span of the frequency domain.

In some multiple-access protocols, more than one approach is used.

In GSM protocol digital mobile radiotelephone systems, MSs and BTSsleverage communications across both frequency and time division multipleaccess (FDMA/TDMA) channels such that MSs can share the same transmitand receive carriers via the assignment of distinct timeslots over eachcarrier frequency and each carrier frequency might be handled by adistinct transceiver or transceiver module or logic block.

In GSM, the BTS is responsible for assigning a timeslot to the mobilestation (MS) when it requests access. In a GSM frame structure, thereare eight timeslots within each TDMA frame. The number of carrierfrequencies used can vary. In some regions, some carriers are licensedfor a large number of carrier frequencies and MSs in those regions areconfigured to accept instructions to use one of as many as a thousandcarrier frequencies (which a BTS would also support). For instance, inEurope the GSM 900 MHz spectrum band comprises 25 MHz of spectrum. Ifthis is logically allocated into 200 kHz carrier frequencies (e.g., acarrier frequency centered within each 200 kHz subspectra band), andtransceivers send signals on those carrier frequencies, this providesfor 125 carrier frequencies. The use of guard bands (unused carrierfrequencies) in the frequency domain might reduce this number, but mightprovide added reliability or ease of signal processing. Where a TDMAframe allows for eight timeslots, a BTS having sufficient numbers oflogical or actual transceivers available, could support 8*125=1000 MSschannels simultaneously. With time division and frequency division,there can be guard slots and guard frequencies, respectively, so thatone division has some separation from an adjacent division. With someprotocols, more than one timeslot and/or more than one carrier frequencycan be assigned to one MS, to provide greater bandwidth.

In some cases, there are multiple BTSs within range of supported MSs andso the support of the MSs can be spread among the BTSs and perhaps theycoordinate so that adjacent BTSs avoid using the same carrierfrequencies when possible. BTSs might be programmed to spread thesefrequencies across their towers with a specific re-use scheme. It mightalso be that a BTS is limited in the number of MSs it can support by thesize of the pipe to the other network resources. In one example, a BTSuses from 1 to 15 carrier frequencies (i.e., its transceivers transmitusing 1 to 15 carrier frequencies in sending/receiving frames, so itcould support anywhere from 8 to 120 simultaneous users.

Each MS typically includes a processor, memory, radio circuitry, a powersource, display, input elements and the like to perform its functions.The processor might read from program memory to perform desiredfunctions. For example, the program memory might have instructions forhow to form a data stream, how to pass that to the radio circuitry, howto read an internal clock to determine the value of a system clock toappropriately time listening and sending, and how to set appropriatefrequencies for transmissions and reception.

Each BTS typically includes a processor, memory, radio circuitry, powersource(s), interfaces to the telecommunications network, diagnosticinterfaces and the like to perform its functions. The BTS processormight read from program memory to perform desired functions. Forexample, the program memory might have instructions for how to form adata stream, how to pass that to the radio circuitry, how to communicatewith the telecommunications network, how to read an internal clock todetermine the value of a system clock to appropriately time listeningand sending, how to set appropriate frequencies for transmissions andreception, how to keep track of the various MSs and their state,location, allocation, etc. and perhaps store that into locally availablememory.

In the manner described above, an MS will contact a BTS to get allocatedsome timeslots in frames in some carrier frequencies and the BTS willinform the MS of the MS's allocation. As both the BTS and the MS havethe same system clock (or approximately so), they will communicatewithin their allotted timeslots and carrier frequencies. The assignmentand communication of the assignments to the MSs might occur using arandom access channel that is used by the MS to request an allocation.In the GSM protocol, this is referred to as a RACH process.

In the example of GSM, communication over the wireless communicationpathway is parsed into TDMA frames of duration 4.61538 ms, with eighttimeslots per TDMA frame. Each timeslot is long enough to hold 156.25bits of data. In one application, the MS or BTS will transmit 148 bitsof data in a timeslot, over 546.46 μs, with 8.25 bits (30.46 μs) of aguard time between timeslots. In the GSM900 Band, the wirelesscommunication pathway has a bandwidth of 25 MHz in the uplink anddownlink directions each, using the spectrum band of 890-915 MHz foruplink subchannels and the spectrum band of 935-960 MHz for downlinksubchannels, providing for 125 carrier frequencies (125 carrierfrequencies in each direction, spaced 200 kHz apart). With 200 kHz ofguard separation on each side of each spectrum band, that leaves 24.6MHz of spectrum, or 123 carrier frequencies, for moving data. The totalcapacity of such a wireless communication pathway (in both directions)would then be 156.25 bits per timeslot times eight timeslots per frametimes 216.667 frames/second*123 carriers=33.312 Mbits/second.

Given that the MSs can be mobile, they might be some distance from theBTS and that distance might be changing, such as where the MSs is beingused to carry on a voice conversation over the telecommunicationsnetwork while the BTS is fixed to a cellphone tower but the MS is 10 kmaway and moving at 100 KPH. If the BTS and MS are within a few meters ofeach other and the MS is not moving, the propagation time of the signalsand the Doppler shift due to movement can be ignored. If the MS ismoving 100 KPH relative to the BTS, perhaps that can be ignored, but ifthe MS is some distance away, the propagation time needs to be takeninto account or else transmissions in one timeslot will not be receivedentirely within that timeslot but might arrive late, in the time ofanother timeslot, which could cause communications losses.

To account for propagation delays, a transmitter will advance or retardthe transmission and send bursts of radio frequency (RF) signals toaccount for propagation delays and a receiver will expect an allocatedtransmission at an adjusted time. Where there are many MSs and one BTSit is often useful for the MSs to be the ones adjusting theirtransmission times, so that the place where the timeslots are allaligned is at the BTS. Likewise, the BTS can send its transmissions inthe designated timeslots, but the MSs will delay or advance the time atwhich they listen or expect to receive a transmission, to account forpropagation delays. It may be that in addition to the BTS allocating atimeslot or slots and a carrier frequency or carrier frequencies to anMS, the BTS will indicate to the MS what the propagation delay ordistance is between the BTS-MS.

For a BTS operating using the GSM protocol, the BTS will know thepropagation delay of a MS signal because of how the signal arrives onthe RACH (Random Access Control Channel). The RACH channel is anuplink-only timeslot that is used when a MS needs to access a channel tosend data. The MS will request channel access by sending a signal burstthat is 87 bits long on the RACH. The RACH burst is designed so thatthere are 69.25 bits of guard period between it and the next timeslot.As a result, the burst can slide within the RACH slot by up to 69.25bits without ill effects. When the RACH burst arrives at the BTS, theBTS can measure how many of these guard bits the signal burst slipped tothe right (i.e., moved out further in time) and thus it can determinethe signal's propagation delay. When the BTS responds to the MS withinformation about its channel assignment, the BTS will include what iscalled a “timing advance” (TA), which might be expressed as a number ofbits that the MS should advance its signal by in order arrive at the BTSwithin the correct timeslot and not bleed into an adjacent timeslot. Inthe GSM protocol, the timing advance value can be anywhere between 0 to63 bits, where 0 bits corresponds to no round-trip propagation delay and63 bits corresponds to the propagation delay that would be experiencedwith a MS that is 35 km away from the BTS with the wireless signalstraveling at the speed of light.

Without careful timing, transmissions from MSs operating at differentdistances can arrive at the BTS within the same timeslot and causecollision or overlap. These collisions create interference from theperspective of the BTS, which disrupts the quality and reliability ofcommunications. Guard time (measured in bits and referred to as “guardbits”) can be employed to prevent burst timing errors from creatingsignal collisions, but this can only account for small time alignmenterrors in internal clocks and cannot account for differences in extendedand variable propagation distances.

For example, there might be 30.461 μs of guard time (8.25 guard bits)between timeslots, so that even if a first MS was 4.569 km away from theBTS (9.138 km in round-trip distance) and assigned a first timeslot anda second MS was right near the BTS and assigned the next timeslot, therelative propagation delays of the signals would not result ininterference. This is because while the signal from the first MS wouldbe delayed by 30.461 μs, the BTS would receive the later part of thetransmission during the guard time, and that transmission would endbefore the second MS's timeslot began. Often, the guard time is tooshort to accommodate MSs at all distances they might be found at. Forexample, if a MS is 10 km (20 km round-trip) away, the propagation delayof a transmission from that MS to the BTS would be delayed by 33.333 μs,which is more than the guard time, so the BTS would be receiving thattransmission at the same time as a transmission from another MS that hasbeen assigned the next timeslot.

One solution to accommodate distant MSs sharing the same BTS is to use atiming advance mechanism. The GSM protocol provides for an example ofthis. In the initial handshake between the MS and the BTS, such as theGSM protocol's uses of a Random Access Channel (RACH) communication, theBTS determines a distance between the MS and the BTS. The BTS mighttransmit and receive timestamps during a RACH handshake in calculating adistance between the MS and the BTS for each MS is based on an uplinkpropagation delay.

The determined distance might not be the actual distance between the MSand the BTS, but for many purposes, a pseudo distance is sufficient. Asused herein a “pseudo distance” is a value that might or might not be anactual value for a distance, but it is used as a proxy or as the deemeddistance, i.e., a module in the MS, the BTS, or elsewhere will assumethat value to be the distance and the various components are designedsuch that using that value works sufficiently well when that value issufficiently close to the actual value. As an extreme example, supposean MS and a BTS are 2 meters apart, but there is something in betweenthem that prevents a direct signal and the closest path is a 3 km paththat involves numerous reflections. In such a case, the pseudo distancewould be 3 km and the MS and BTs would operate assuming that they areseparated by 3 km. Since the signal path that their transmissions followis 3 km, using that as the value for the distance between them works.

In general, a pseudo distance, or pseudo range of distances, that ismeasured between two objects might differ from their actual distance orrange of distances might be measured by determining the time it takesfor a radio frequency signal to propagate from one object to the other.Due to signal reflection and multipath, the line of sight distance (orrange of distances) between the origin of a signal and its recipient canbe slightly different from the propagation distance of that signal, inwhich case the pseudo distance (or range of pseudo distances) variesfrom the actual distance (or range of distances). But with consistentuse, many operations can work with just value of the pseudo distance. Inother uses, “pseudo” might be similarly used to indicate an estimate,assumed, approximate, etc. value.

Once the BTS determines the pseudo distance for an MS, the BTS stores apseudo distance in a table that the BTS maintains for parameters andvariables for each of the active MSs using the transceivers of that BTS.The BTS will communicate that value to the MS in a control message as isdescribed elsewhere herein. The MS then is programmed to implement a“timing advance” wherein the MS considers its copy of the system clock,subtracts a propagation delay corresponding to the pseudo distance andsends its transmission to the BTS earlier than the start of itsscheduled timeslot. A RACH process might include various steps asdescribed in further detail below to determine these values.

As used herein, a propagation delay can be calculated from a propagationdistance and vice versa, using c=3*10⁸ m/s as the conversion factor oran approximation thereto. Where there is a standardized bit rate fortransmissions, such as 270.833 kbits/s for GSM, the propagation delay ordistance can be expressed as a number of bits. For example, a 12 kmseparation would result in a round-trip propagation delay of 80 μs andwith each bit being transmitted over 3.692 μs, the 12 km separation andthe propagation delay of 80 μs could be equivalently represented asbeing a separation or propagation of 22 bits (21.66 to be more precise).Thus, one “bit” of propagation would be equivalent to around 555 metersof round-trip propagation distance and 3.692 μs.

MSs operating at different distances from the BTS will be assigneddifferent timing advances to accommodate their respective communicationdistances. For convenience, this might be expressed as an integer numberof bits. To account for MS movement, this timing advance value, which iscommunicated to the MS and is used by modules in the MS to determinewhen to transmit or receive, might be updated periodically andfrequently enough to accommodate moving targets that might have atime-variant communication distances relative to the BTS. For example,where a user is using a MS on a high-speed train traveling at 200 KPH,the distance might need to be updated more frequently than if the useris walking on a street.

In the specific example of the GSM protocol, the timing advance isrepresented as a 6-bit value where the minimum value represents a 0-bittiming advance and the maximum value represents a 63-bit timing advance.Since each bit in the GSM protocol is assumed to correspond to 3.692 μs(and about 555 meters in round-trip propagation delay), 63 bits oftiming advance would be used where the pseudo distance is around 555m/bit*63 bits=34,965 m, or about 35 km. Thus, this timing advanceapproach would work fine for MSs that are between 0 and 35 km from theBTS. In the GSM protocol, BTS are programmed to, or at least expectedto, not respond to requests from a MS if the BTS determines that the MSis further than 35 km from the BTS. This is not a problem when there areother closer BTSs or a distribution of BTSs where all points are within35 km of one or more BTS.

With a timing advance, the MS sends a transmission before its timeslotbegins (from the MS's clock timing) and when it is received at the BTSafter a propagation delay, the BTS receives it entirely within itstimeslot when the timing advance corresponds to the propagation delay.The MS can correctly do this, because it has been provided a value forhow much of a timing advance to use. Note that the actual distance, andtherefore the actual propagation delay, might vary from the pseudodistance, but that is often not a problem since the MS-BTS communicationhas some leeway that is there to handle internal clock differences,transmitter variances, etc.

That timing mechanism works well when there is always one or more BTSwithin 35 km of any MS, but this might not always be the case. In somegeographic regions, it might not be practical, feasible, or economicalto have BTSs no more than 35 km from any point in the region. Forexample, in rural, remote, or island geographic regions, BTSinfrastructure with such spacing might leave BTSs unused or unable to beinstalled or obtain electrical power, as the terrain might beinaccessible and users with MSs might be sparse and widespread. In suchsituations, an “extended range” mechanism might be used. The GSMprotocol allows for such a mechanism.

With an extended range mechanism, each MS is assigned two consecutivetimeslots instead of one, so an MS can communicate with a BTS withoutneeding any timing advance, as the transmission can be delayed at theBTS by as much as the duration of one timeslot. While this increasesallowed MS-BTS distance (e.g., from 35 km to 120 km), it decreasesthroughput by half, as there would be only four assignable timeslotsavailable in each TDMA frame instead of eight. This might not be aconcern in rural, remote, or island areas, if data rates are low. Byusing a combination of the timing advance mechanism and the extendedrange mechanism, the maximum allowed MS-BTS could be 35 km+85 km =120km.

With the extended range mechanism, each MS is allotted an entiretimeslot as an additional guard period, which reduces the throughput byhalf. A variation of this is the “sorted extended range mechanism”similar to that shown in, for example, U.S. Pat. No. 5,642,355. With thesorted extended range mechanism, timeslots are “consumed” to be used asguard bits, but the timeslots are assigned to MSs by distance, with theclosest MS getting the first timeslot and the furthest MS getting thelast timeslot that is allotted to an MS, i.e., before any “consumed”timeslots that are not assigned to any MSs. The consumed timeslots areused for guard bits that are needed since the extended range of the MSswill spread out the transmissions. In effect, this “divides up” unusedtimeslots between the bursts.

If there is more than an 85 km gap, or for other reasons, a “ringextended range” mechanism might be used. With the ring extended rangemechanism, a fixed minimum distance is assumed, the timing at the BTS isadjusted by that fixed minimum distance, and a MS that is closer thanthe minimum communication distance is not supported, as the BTS assumesthat all MSs are at least that distance away. This is similar to theapproach shown in U.S. Pat. No. 6,101,177. The 35 km range obtainedusing the timing advance mechanism can be used to support a MS-BTSdistance that ranges from the minimum distance to the minimum distanceplus 35 km without requiring any MS modifications. In one example, theminimum distance is 85 km, but a different minimum communicationdistance might be used. In that example, then, the BTS could support anMS that is between 85 km and 120 km from the BTS.

The ring extended range mechanism can be used with 8 of 8 timeslotsallocated and can handle MSs with distances that range from 85 km to 120km from the BTS. However, this creates a physical coverage gap someradius away from the BTS because any signal burst sent from that areawill arrive at the BTS too early relative to how the BTS views itstimeslots. Instead, the BTS provides coverage for a ring of area. Thering extended range mechanism might be used in geographic areas thathave physical gaps, such as lake or valleys, between the BTS and the MSsthat it is designed to service, so it would not be a problem to have aregion inside the ring where no MSs are supported.

It should be noted that the GSM system employs a TDMA frame offsetbetween uplink and downlink subchannels. In a typical GSM framestructure, the uplink TDMA frame (or MS Tx and BTS Rx) is offset fromthe Downlink TDMA frame (or BTS Tx and MS Rx) by three timeslots for thepurpose of ensuring that the MS does not need to transmit and receive atthe same time. It will be clear to those skilled in the art of TDMAcommunications that this offset between uplink and downlink subchannelsis independent of communications over extended distances and is not thesame as the timeslot synchronization offset used on the uplink TDMAframe only in the ring extended range mechanism.

If the ring extended range mechanism is combined with the extended rangemechanism, this can be used, alone or in combination, to have a BTScoverage that might be over a 120 km radius. These techniques are oftensufficient for terrestrial communications, as such communications aretypically limited by Earth curvature. For example, to provide line ofsight communications between a ground-based MS and a BTS transceiver Ddistance away, the BTS transceiver should be mounted at a height of atleast h=[SQRT(6370{circumflex over ( )}2+D{circumflex over ( )}2)−6370]km. For D=120 km, h=1130 m. As 1,130 meters is higher than any structurebuilt today, tower height is much more of a limiting factor forterrestrial communications than distance and so techniques for extendingdistance further than say 120 km are not that useful for terrestrialcommunications for cellular voice, data, text, and similar capabilities,except possibly in selected locations where there are large geologicstructures upon which to mount transceivers.

For regions where it is not practical to have base station towersdistributed so that there is broad coverage, such as where it isimpractical to locate a base station anywhere near some locations, suchas within 35 km or 85 km from some location or 120 km where elevatedtowers can be mounted, satellite communications might be used.Typically, satellite communications is very expensive and thus only usedin applications that support the costs, such as resource exploration,explorers, search and rescue, and the like.

Herein, “satellite” refers to an artificial satellite that is launchedfrom Earth with a goal of operating in orbit and/or that operates inorbit whether assembled in whole or part on the ground and/or assembledin whole or part in orbit. A satellite might be assembled and/or operatein one orbit and move to another orbit. The satellite might be propelledor be operating without its own means of propulsion and might or mightnot rely on other objects in orbit to provide propulsion. As usedherein, a satellite when in operation in orbit and not under propulsionis in an orbit that is more or less stable. Such orbits have a minimumdistance above the surface of the Earth due to atmospheric drag. Thereis not a strict dividing line between sufficient vacuum to allow fororbiting and excessive atmosphere that would cause the deorbiting of asatellite, by Low Earth Orbit (LEO) of around 400 to 500 km above theEarth have been shown to be practical, but could be even lower thanthose altitudes for particularly dense spacecraft such asnanosatellites.

The minimum distance for a practical orbit being so large hastraditionally meant that entirely different technologies were employedin satellite communications. In some cases, the ground stations were notmobile and in other cases, they were mobile but requiredpower-intensive, heavy, large and specialized equipment. In addition todistance, movement of the satellite in orbit had to be addressed.

There are many solutions for communications between satellites andground-based portable handsets on Earth that use that TDMA protocols forcommunications. Some satellite providers include Iridium™, Globalstar™,Thuraya™, and Inmarsat™ satellite systems, which are based on a uniquelydeveloped satellite phone or user terminal (i.e., a unique hardwaredevice that attaches or connects to an existing mobile phone by aphysical or RF connection). With a specific user terminal, the design ofthe system, the satellite and the terminal can be simplified, as eachcan be designed specifically to work with the others. The downside isthat it requires specific terminal equipment, which would be needed forevery end user or small groups of end users, which can becost-prohibitive and unwieldy. While the custom terminal approachsimplifies the system design, as the operator is free to set the detailsfor communication methods, power levels, frequencies, and the like, thisties the users to specific providers. As a result, the end user mightneed to purchase a satellite phone (or a user terminal that plugs intoan existing mobile phone) that costs hundreds to thousands of dollars,is large, has a cumbersome antenna, uses significant power, and has asteep monthly service subscription to operate, and may have to do thisfor more than one satellite provider. This has limited the appeal of theclassic satellite phone market.

As an example, U.S. Pat. No. 8,538,327 describes a modification to userequipment computes a delay measure based on data indicative of theposition of a satellite and data indicative of the position of the userequipment. Timing of uplink communication from the user equipmentadjusts for that delay when transmitting up to the satellite. The userequipment also computes a frequency offset based on data indicative ofthe position and velocity of the satellite and adjusts its uplink signalfrequency accordingly to account for dynamic Doppler shift in thecommunications system. This, of course, requires specific user equipmenton the ground that is designed for satellite communications.

As another example, U.S. Patent Publication 2006/0246913 describes amethod for managing propagation delay of RF signals using sub-coveragerings characterized by reduced difference in round-trip propagationdelay differences. This uses a geosynchronous Earth orbit (GEO)satellite to act as a relay to connect a remote mobile station with abase station in its network. To deal with the much greater delays that aGEO satellite introduces, separate processing devices service separatesub-coverage ring, or zone, by configuring itself for that ring's/zone'srange of allowable propagation delays. The link between a mobile stationand a GEO satellite cannot be closed without the assistance ofadditional user terminal hardware for power, signal directivity, andfrequency manipulation.

What is needed is an improved system for satellite-based communicationswith portable or mobile devices.

SUMMARY

A multiple-access transceiver for communications with mobile stations inenvironments handles conditions that exceed mobile station designassumptions without necessarily requiring modifications to the mobilestations, as might be found in Earth orbit. The multiple-accesstransceiver is adapted to close communications with mobile stationswhile exceeding mobile station design assumptions, such as greaterdistance, greater relative motion and/or other conditions commonly foundwhere functionality of a terrestrial transceiver is to be performed byan orbital transceiver. The orbital transceiver might include a dataparser that parses a frame data structure, a signal timing module thatadjusts timing based on orbit to terrestrial propagation delays,frequency shifters and a programmable radio capable of communicatingfrom the Earth orbit that uses a multiple-access protocol such that thecommunication is compatible with, or appears to the terrestrial mobilestation to be, communication between a terrestrial cellular base stationand the terrestrial mobile station.

The multiple-access transceiver might support terrestrial mobilestations that are cellular telephone handsets, smartphones, and/orconnected devices. The signal timing module might be adapted to adjustfrequency of the transmitted signals based on orbit to terrestrialDoppler shifts. The signal allocation logic might allocate capacity ofthe multiple-access transceiver to a plurality of terrestrial mobilestations, including the terrestrial mobile station, distributed over aplurality of timeslots, a plurality of carrier frequencies, a pluralityof orthogonal subcarriers and/or a plurality of code sequences. Themultiple-access transceiver might include a range calculator thatdetermines, for each terrestrial mobile station, a distance from themultiple-access transceiver to the terrestrial mobile station and asignal timing module that determines timing of transmitted signalsrelative to the frame structure, wherein the frame structure comprises aplurality of slots each having a zero or nonzero timeslotsynchronization offset that provides for variable transmission delaysthat are due to the distance from the multiple-access transceiver to theterrestrial mobile station, and an input signal allocator that allocatesa listening timeslot in the frame structure to listen for communicationsfrom the terrestrial mobile station where the listening timeslot istimed based on the distance from the multiple-access transceiver to theterrestrial mobile station and the listening timeslot is one of aplurality of timeslots that are variably delayed in the frame structureto account for the multiple-access transceiver handling communicationsfrom a plurality of terrestrial mobile stations having a plurality ofdistances from the multiple-access transceiver.

The multiple-access transceiver might have the plurality of timeslotsvariably delayed in the frame structure to account for themultiple-access transceiver handling communications from a plurality ofterrestrial mobile stations having a plurality of distances from themultiple-access transceiver by assigning each of a plurality ofdifferent distance ranges to each of a plurality of channel blocks. Thedifferent distance ranges might collectively cover a slant range from azenith distance through a minimum elevation distance, wherein the zenithdistance is a distance between a zenith position of a satellite carryingthe multiple-access transceiver relative to a terrestrial mobile stationand wherein the minimum elevation distance is a distance between aposition of the satellite when the terrestrial mobile station enters adesign footprint of the satellite. The different distance ranges mightspan approximately 34 to 35 kilometers each, with a difference between azenith distance and a low elevation distance of between 210 and 250kilometers. The design footprint of a satellite might be a circle,ellipse, rectangle and/or be is independent of, or a function of anantenna and/or antenna beam shape, but in many examples it isapproximated as a circle.

A multiple-access transceiver might be adapted for operation in Earthorbit and configured for communication with terrestrial mobile stations,comprising a data parser that parses data received by themultiple-access transceiver according to a frame structure, wherein theframe structure defines which timeslots are allocated to whichterrestrial mobile stations, a range calculator that determines, foreach terrestrial mobile station, a distance from the multiple-accesstransceiver to the terrestrial mobile station, a channel assignmentmodule that assigns a plurality of terrestrial mobile stations to aplurality of channel blocks, wherein a channel block has a terrestrialfrequency and an orbital frequency offset, a signal timing module thatdetermines timing of transmitted signals relative to the framestructure, and a signal modulator that modulates signals to aterrestrial mobile station at the terrestrial frequency with the orbitalfrequency offset, wherein the orbital frequency offset at leastapproximately corresponds with an expected Doppler shift in signalstransmitted to the terrestrial mobile station due to relative movementof the multiple-access transceiver and the terrestrial mobile station sothat the terrestrial mobile station receives the signal at theterrestrial frequency. The plurality of channel blocks might beallocated based on relative positions of a satellite carrying themultiple-access transceiver and the terrestrial mobile station where theorbital frequency offset varies in small increments, such as 5 kilohertzincrements.

In a specific embodiment, a multiple-access base station with one ormore transceiver handles communication with a plurality of terrestrialmobile stations, wherein a terrestrial mobile station is configured toexpect base station communications with a terrestrial cellular basestation that is within a limited distance from the terrestrial mobilestation and/or that is moving less than a limited velocity relative tothe terrestrial mobile station. The multiple-access base stationcomprises a data parser that parses data received by the multiple-accessbase station according to a frame structure, wherein the frame structuredefines which timeslots are allocated to which of the plurality ofterrestrial mobile stations, wherein the frame structure comprises aplurality of slots each having a zero or nonzero timeslotsynchronization offset that provides for variable transmission delaysthat are due to a distance from the multiple-access base station to theplurality of terrestrial mobile stations; a signal timing module thatdetermines a signal timing adjustment relative to the frame structurefor a transmitted signal to the terrestrial mobile station based on abase-to-mobile distance between the multiple-access base station and theterrestrial mobile station where the base-to-mobile distance exceeds thelimited distance; and a programmable radio capable of communicating acommunication from the multiple-access base station to the terrestrialmobile station using a multiple-access protocol and taking into accountthe signal timing adjustment, such that the communication is compatiblewith, or appears to the terrestrial mobile station to be, communicationbetween a terrestrial cellular base station and the terrestrial mobilestation, notwithstanding that the base-to-mobile distance exceeds thelimited distance.

The multiple-access base station might be adapted to communicate withthe plurality of terrestrial mobile stations wherein the plurality ofterrestrial mobile stations comprises cellular telephone handsets,smartphones, and/or connected devices. The limited distance might bearound 100 kilometers, 120 kilometers or some other distance, with thebase-to-mobile distance exceeding that limited distance. Themultiple-access protocol might be one of a CDMA-based protocol, an LTEprotocol, a GSM protocol, an OFDMA-based protocol, an FDMA-basedprotocol, a TDMA-based protocol, an EGPRS protocol, or an EDGE protocol.The multiple-access base station might be an orbital base station to beoperated in Earth orbit, where the limited distance is 120 kilometersand base-to-mobile distances of terrestrial mobile stations of theplurality of terrestrial mobile stations are from about 500 kilometersto about 750 kilometers. In another variation, multiple-access basestation is a base station operable in Earth atmosphere, including beingmounted on or in one or more of an airplane, a drone, and/or a balloon,wherein the limited distance is 120 kilometers and the base-to-mobiledistance exceeds 120 kilometers.

The multiple-access base station may include signal allocation logic toallocate capacity of the multiple-access base station to the pluralityof terrestrial mobile stations, including the terrestrial mobilestation, distributed over a plurality of timeslots, a plurality ofcarrier frequencies, a plurality of orthogonal subcarriers and/or aplurality of code sequences. The programmable radio might be capable oflistening for communications from the terrestrial mobile station using amultiple-access protocol and include a range calculator that determines,for each terrestrial mobile station of the plurality of terrestrialmobile stations, its base-to-mobile distance from the multiple-accessbase station to the terrestrial mobile station; a receive timing modulethat determines timing of received signals of the terrestrial mobilestation relative to the frame structure based on the terrestrial mobilestation's base-to-mobile distance; and an input signal allocator thatallocates a listening timeslot in the frame structure to listen forcommunications from the terrestrial mobile station where the listeningtimeslot is timed based on the terrestrial mobile station'sbase-to-mobile distance and the listening timeslot is one of a pluralityof timeslots that are variably delayed in the frame structure to accountfor the multiple-access base station handling communications from theplurality of terrestrial mobile stations having a plurality ofbase-to-mobile distances.

The plurality of timeslots might be variably delayed in the framestructure to account for the plurality of terrestrial mobile stationshaving a plurality of base-to-mobile distances by assigning each of aplurality of different base-to-mobile distance ranges to each of aplurality of channel blocks. The multiple-access base station can be anorbital base station to be operated in Earth orbit, where the pluralityof different base-to-mobile distance ranges collectively cover a slantrange from a zenith distance through a minimum elevation distance,wherein the zenith distance is a distance between a zenith position of asatellite carrying the multiple-access base station relative to aterrestrial mobile station and wherein the minimum elevation distance isa distance between a position of the satellite when the terrestrialmobile station enters a design footprint of the satellite.

The different base-to-mobile distance ranges might each spanapproximately 34 to 35 kilometers with a difference between the zenithdistance and the minimum elevation distance is between 210 and 250kilometers.

The design footprint of the satellite might be a circle, ellipse,rectangle, etc., and might be independent of, or a function of anantenna and/or antenna beam shape.

In some variations, the multiple-access base station having one or moretransceiver handles communication with a plurality of terrestrial mobilestations configured to expect base station communications with aterrestrial cellular base station that is within a limited distance fromthe terrestrial mobile station and/or that is moving less than a limitedvelocity relative to the terrestrial mobile station. The multiple-accessbase station comprises a data parser that parses data received by themultiple-access base station according to a frame structure, wherein theframe structure defines which timeslots are allocated to which of theplurality of terrestrial mobile stations, and according to amultiple-access protocol in which the terrestrial mobile station expectsto receive signals at a specified frequency and to transmit signals at aspecified frequency; a Doppler shift calculator that determines, foreach terrestrial mobile station of the plurality of terrestrial mobilestations, its Doppler shift due to velocity of it relative to themultiple-access base station; a channel assignment module that assignseach of the plurality of terrestrial mobile stations to channel blocksin a plurality of channel blocks, wherein each a channel block has aterrestrial frequency and a Doppler frequency offset; a signal modulatorthat modulates signals to the terrestrial mobile station at theterrestrial frequency with the Doppler frequency offset, wherein theDoppler frequency offset at least approximately corresponds with anexpected Doppler shift in signals transmitted to the terrestrial mobilestation due to relative movement of the multiple-access base station andthe terrestrial mobile station so that the terrestrial mobile stationreceives the signal at the terrestrial frequency; and a programmableradio capable of receiving a communication from the terrestrial mobilestation using the multiple-access protocol and taking into account theDoppler frequency offset of the terrestrial mobile station, such thatthe communication is compatible with, or appears to the terrestrialmobile station to be, communication between a terrestrial cellular basestation and the terrestrial mobile station, notwithstanding that thevelocity of the terrestrial mobile station relative to themultiple-access base station exceeds the limited velocity.

The velocity of the terrestrial mobile station relative to themultiple-access base station might be a result of the multiple-accessbase station being in Earth orbit the Doppler frequency offset mightvary in 5 kilohertz increments.

The multiple-access base station might have signal allocation logic toallocate capacity of the multiple-access base station to the pluralityof terrestrial mobile stations, including the terrestrial mobilestation, distributed over a plurality of timeslots, a plurality ofcarrier frequencies, a plurality of orthogonal subcarriers and/or aplurality of code sequences.

The multiple-access base station might provide, for each of theplurality of channel blocks, an uplink subchannel and a downlinksubchannel, with a contiguous spectrum for uplink subchannels and acontiguous spectrum for downlink subchannels. The channel blocks mightbe assigned such that adjacent channel blocks are assigned to adjacentDoppler frequency offsets.

In a specific embodiment of a multiple-access base station having one ormore transceiver that handles communication with a plurality ofterrestrial mobile stations, wherein a terrestrial mobile station isconfigured to expect base station communications with a terrestrialcellular base station that is within a limited distance from theterrestrial mobile station and/or that is moving less than a limitedvelocity relative to the terrestrial mobile station, the multiple-accessbase station might include a data parser that parses data received bythe multiple-access base station according to a frame structure, whereinthe frame structure defines which timeslots are allocated to which ofthe plurality of terrestrial mobile stations, wherein the framestructure comprises a plurality of slots each having a zero or nonzerotimeslot synchronization offset that provides for variable transmissiondelays that are due to a distance from the multiple-access base stationto the plurality of terrestrial mobile stations and further according toa multiple-access protocol in which the terrestrial mobile stationtransmits at a expects to receive signals at a specified frequency andto transmit signals at a terrestrial frequency and is received with aDoppler frequency offset, and wherein the multiple-access protocolspecifies channel blocks in a plurality of channel blocks wherein each achannel block has a designated terrestrial frequency and a designatedtimeslot; a signal timing module that determines a signal timingadjustment relative to the frame structure for a transmitted signal tothe terrestrial mobile station based on a base-to-mobile distancebetween the multiple-access base station and the terrestrial mobilestation where the base-to-mobile distance exceeds the limited distance,wherein each channel block is assigned a designated signal timingadjustment; a Doppler shift calculator that determines, for eachterrestrial mobile station of the plurality of terrestrial mobilestations, its Doppler shift due to velocity of it relative to themultiple-access base station and each channel block is assigned adesignated Doppler frequency offset; a dynamic channel allocator thatallocates each of the plurality of terrestrial mobile stations to adesignated channel block in the plurality of channel blocks based on itsdesignated signal timing adjustment and its designated Doppler frequencyoffset, with a number of channels in the designated channel blockcorresponding to a number of the plurality of terrestrial mobilestations that have, or are expected to have, a designated signal timingadjustment and designated Doppler frequency offset; a signal modulatorthat modulates signals to the terrestrial mobile station at theterrestrial frequency with the Doppler frequency offset, wherein theDoppler frequency offset at least approximately corresponds with anexpected Doppler shift in signals transmitted to the terrestrial mobilestation due to relative movement of the multiple-access base station andthe terrestrial mobile station so that the terrestrial mobile stationreceives the signal at the terrestrial frequency; and a programmableradio capable of receiving a communication from the terrestrial mobilestation using the multiple-access protocol and taking into account theDoppler frequency offset of the terrestrial mobile station, such thatthe communication is compatible with, or appears to the terrestrialmobile station to be, communication between a terrestrial cellular basestation and the terrestrial mobile station, notwithstanding that thebase-to-mobile distance exceeds the limited distance and notwithstandingthat the velocity of the terrestrial mobile station relative to themultiple-access base station exceeds the limited velocity.

The following detailed description together with the accompanyingdrawings will provide a better understanding of the nature andadvantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments in accordance with the present disclosure will bedescribed with reference to the drawings, in which:

FIG. 1 illustrates an environment in which the present invention mightbe used.

FIG. 2 illustrates additional examples for the environment of FIG. 1.

FIG. 3 illustrates an example of a frame-based protocol used between abase transceiver station and a mobile station.

FIG. 4 shows an example of an effect of propagation delay and the use ofa timing advance when using a time-division protocol.

FIG. 5 shows an example of the use of an extended range feature of atime-division protocol.

FIG. 6 shows an example of the use of an extended range feature of andtiming advance with a time-division protocol.

FIG. 7 shows an example of a variety of MSs at different distances froma BTS where those distances are determined, at least approximately.

FIG. 8 illustrates how various MSs at different distances in FIG. 7 areassigned timeslots based on their determined distances to provide forsorted extended range communications.

FIG. 9 illustrates a coverage area for a ring method using asynchronization offset.

FIG. 10 illustrates how timing is adjusted for the ring method.

FIG. 11 illustrates an example of a satellite footprint and theresulting distance ranges within that satellite footprint.

FIG. 12 shows an example of how different mobile stations might beassigned different timeslots based on their terrestrial location toimplement a ring method and a sorted extended range method for TDMAcommunications.

FIG. 13 illustrates how different mobile stations might be assigneddifferent carrier frequencies based on their terrestrial locationdistances so that the ring method can be used with varying ringdiameters for different carrier frequencies.

FIG. 14 shows how a satellite footprint might be subdivided into Dopplershift strips.

FIG. 15 is a flowchart of a measurement process to determine a pseudodistance and a Doppler shift from a MS.

FIG. 16 shows how a satellite footprint might be subdivided into rangerings, into Doppler shift strips, and into both range rings and Dopplershift strips.

FIG. 17 illustrates an example of range ring/Doppler shift cells of asatellite footprint.

FIG. 18 illustrates an example assignment of the range ring/Dopplershift cells of FIG. 17 to particular carrier frequencies and Doppleroffset blocks.

FIG. 19 illustrates how frequency spectra might be allocated to thevarious Doppler offset blocks for a channel considering the Dopplershifts in communication between the BTS and the MSs.

FIG. 20 illustrates an example assignment of cells of a satellitefootprint based on anticipated density of MSs by cell.

FIG. 21 illustrates an example channel allocation that might be used forthe allocation and mapping illustrated in FIG. 20.

FIG. 22 is a swim diagram illustrating a process for setup and distancedetermination.

FIG. 23 illustrates an example transceiver and related components.

DETAILED DESCRIPTION

In the following description, various embodiments will be described. Forpurposes of explanation, specific configurations and details are setforth in order to provide a thorough understanding of the embodiments.However, it will also be apparent to one skilled in the art that theembodiments may be practiced without the specific details. Furthermore,well-known features may be omitted or simplified in order not to obscurethe embodiment being described.

Techniques described and suggested herein include designs for asatellite-based base transceiver station (BTS) that is a satellite, orpart of a satellite, that can operate in an orbit, and that implementstransceivers for transmission and reception between ground-baseddevices, such as mobile stations (MSs) that are mobile stations designedto be used with terrestrial BTSs. In many cases, the MSs can be usedwithout requiring any physical modifications or even any softwaremodifications, in which case an MS could be communicating with atransceiver and a BTS and not be aware that the BTS is not a terrestrialBTS, or more generally, that the BTS is operating outside of designassumptions for the MSs, such as being at relative distances greaterthan the design assumption for distance, relative speeds being muchgreater than the relative speed that the MS would be designed for, andother design assumptions.

With orbital transceivers and terrestrial MSs, the BTS would be outsidea design assumption of the MS design that assumes a maximum distancefrom BTS to MS of, say, around 35 km and would be outside a designassumption of the MS design that assumes that relative motions, such asthe time derivative of the BTS-MS distance when communicating, could beignored or is much smaller than the 7.2-7.8 km/s that would beexperienced relative to an orbital transceiver. Other design assumptionsmight also come into play. For example, an orbital transceiver will havea limited time window in which to communicate, as the satellite risesabove a minimum elevation relative to a MS until it sets below theminimum elevation at the opposite horizon.

While most of the examples and details here relate to an orbitaltransceiver that is adapted, configured, programmed, etc., to closecommunications with MSs that operate as if those design assumptionsstill hold true, these techniques can be used beyond just the orbitalexample. For example, they might be used for BTSs that are located highenough that the slant angle is greater than 120 km. For example, if aBTS is able to be mounted at an altitude of 1,130 meters, that is enoughto allow for a line of sight (slant range) to an MS of 120 km or more.Platforms such as airplanes, UAVs, high altitude drones, hot airballoons, high altitude balloons, suborbital vehicles, space planes,mountains, or even some very large towers might be conditions where someor all of these techniques would find utility. It is also worth notingthat the techniques described could even be deployed on a ground basedBTS but with an antenna pointing to provide services to MSs operating onplatforms that create long communication distances (such as in excess of120 km) and/or high Doppler shift environments, such as greater thanaround 200 KPH). This might include conditions in which the MS isoperating on the ground, in the atmosphere, or in a space environmentand the BTS is on the ground and either mobile (e.g., on some vehicle)or perhaps stationary.

These techniques might also find utility where the MS is in orbit andneeds to operate as if the design assumptions are true and the BTS isterrestrial and can operate without the design assumptions being trueand adjust to accommodate those MSs. For example, a MS might be used ina moving airplane, or perhaps a future space station. A base stationtower on the ground with a large enough antenna could perform theoperations to close communications with the MS while addressing similardesign assumption violations, such as long distances and high Dopplershifts.

The BSC and MSC (including home location register, or HLR, andsubscriber handling) functionality might also be supplied in thesatellite, or some of the functionality not needed in orbit specificallyis implemented terrestrially. The BTS, BSC, and/or MSC functionalitymight be implemented using conventional off-the-shelf software-definedradios, or commercial-grade (or proprietary) hardware/software, so longas it can be programmed, configured or adapted to perform necessaryfunctions.

A BTS can provide its functionality despite the extended distancebetween the BTS and the MS that causes power reductions due to distanceand time of flight delays due to distance, and also despite the effectsof greater relative movement between the BTS and the MS that exceedstypical ground-based relative movements that a MS might make relative toa BTS. The latter causes Doppler shifts and a conventional MS, such as acellphone, might not be designed to handle as great a Doppler shift asthat caused by a satellite moving relative to the MS at perhaps a speedof 7.6 km/s experienced in LEO. Those Doppler shifts would be variable,as it varies with the location of the MS within a satellite's footprint.Locations behind the satellite will see negative Doppler shift, whilethose in front of the satellite will see positive Doppler shift.

Power levels should be addressed. As an example, the GSM specificationcalls for mobile phones to surge transmit power to 1 or 2 W (dependingon the frequency) when they need to. The mobile phone will do thisnaturally on the RACH and once it has a channel assigned, the BTS cancommand it to quiet down if it doesn't need to transmit so “loud”. Withsuitable BTS antenna capability, two watts can be enough transmit powerto close the link at a reasonable elevation angle at 500 km altitudeusing antennas in something like a 50 cm form factor, where the speedsof data transfer are adjusted as needed. For example, an implementationmight focus on 2G speeds and narrowband messaging with short databursts, rather than trying to support data rates such as 4G LTE,although the latter might be possible. In such a manner, lower powerlevels and higher data rates can still technically be supported by aspace-based base station with sufficient antenna technology. However,lower the power levels of the ground devices and faster data rates tendto increase the power requirements and mass requirements for the spacesegment.

As used herein, “footprint” refers to the area on the ground that iswithin range to close a communications channel with a BTS on asatellite. In examples herein, circular footprints are used, but itshould be understood that the footprints might not be circular and mightdepend on obscuring factors, shape of the surface of the Earth,atmospheric conditions, etc. In some instances, the footprint is a“design footprint” that is different than an actual footprint. Forexample, a satellite might actually be able to communicate with a mobiledevice that is some distance away and thus within the actual footprintof the satellite, but for selectivity, performance, or other reasons, asystem that uses that satellite is designed for a different footprint,such as a smaller footprint than the actual footprint, that is thedesign footprint. A boundary of a design footprint might be the circleor ellipse cast onto the Earth by the satellite centered on the surfacepoint just below the satellite and having a radius that the satellite issupposed to cover by design, such a certain slant range.

As used herein, “ground” is used to refer to the location of an MS, butit should be understood that “ground” is not limited to the surface ofthe Earth. When an MS is described as being ground-based, or on theground, it could be in the hands of a person standing on the surface ofthe Earth, on the surface of a body of water, somewhat below the surfaceof the Earth or somewhat below the surface of a body of water, in anupper floor of a building, in a structure that is not exactly at groundlevel, in an airplane or otherwise aloft but in the atmosphere, orsimilar locations. However, for clarity of exposition, the MS might bedescribed as being on the ground to distinguish from elements being inorbit. This is not to say that the systems described herein would not beusable for an MS that is in orbit. Where applicable, unless otherwisenoted, MSs in orbits might also be supported, assuming that the devicesare electrically, mechanically, and otherwise, rugged enough for orbitaluse, even if they are not modified specifically to communicate with aBTS in orbit.

As used herein, “being in orbit” refers to being at a location andtravelling at a speed relative to an inertial frame that is stationary(more or less) with respect to the center of gravitation of the Earthand experiences sufficiently little atmospheric drag at that locationsuch that the orbit can be easily maintained. In some examples herein,an orbital distance is given and that refers to, approximately, atypical distance from an average or ordinary point on the surface of theEarth, as is conventional for describing orbits. “LEO” is used in someexamples, and it should be understood that the examples might apply toorbits that might be somewhat outside what is conventionally defined asLEO, but still considered to be orbits. Unless otherwise indicated,being in orbit can also describe orbits around other celestial bodies,such a Mars, the Moon, other planetary moons, or even points ofinterest, such as L1 or L2. In many of the examples herein, the BTS isin orbit around the Earth and the MS is terrestrial. It is possible touse the teachings herein for other situations, such as where the BTS andthe MS switch places, or where instead of in Earth orbit, the BTS is inan airplane, an unpiloted autonomous vehicle, a balloon, etc. wheresimilar difficulties are encountered or more generally where conditionare present in which difficulties, such as distances, propagationdelays, and/or Doppler shifts exceeds what a MS is typically designed tosupport or experience, e.g., the design assumptions that go intoconstructing and/or programing an MS.

In a classic TDMA communications system, there are timing and signalpower aspects to closing a communication link, i.e., creating conditionswhere the received signal power is high enough above thenoise/interference environment such that data can flow over a channel ata desired data rate and bit error rate and following the expectedprotocols such that the devices communicating do not give up at eitherend. As described herein, a satellite-based BTS can communicate with aground-based MS designed for use with ground-based BTSs. Thesatellite-based BTS modifies TDMA communications with MSs in a mannerthat allows for communication over some differential distance byaccounting for variable propagation delays while being transparent tothe MSs. Being in LEO, a constellation of satellites can providecontinuous connection from orbit of 400-500 km above the Earth, with anacceptable economic deployment cost and reasonable service lifetime, toMSs that use conventional terrestrial communications technology andprotocols. The BTS provides suitable timing for TDMA frame structuresthat allows for orbital-range communications and a channel allocation orassignment scheme supporting needed ranges of pseudo distances andDoppler shift mitigation, and deals with signal interference issues andmismatch associated with Doppler shift due to orbital velocities. As aresult, a BTS as described herein can provide communications betweenspacecraft and terrestrial telecommunications devices, andcommunications using features and facilities of the terrestrialtelecommunications devices that are typically used for terrestrialtelecommunications. This can extend the range of radio coverage in acommunication system to enable communications between on-orbitspacecraft and mobile phones or other communication/wireless devices.The BTS can be used in communications systems that leverage multipleaccess techniques in the frequency and/or time domain (i.e., TDMA, FDMA,OFDMA, etc.) used with conventional mobile phones to communicate withspacecraft in orbit using the GSM cellular communication protocols orsimilar terrestrial protocols.

The BTS can be implemented using communication modalities that use amultiple access method in the time and/or frequency domain such as TDMA,FDMA, CDMA, OFDMA, etc. as the BTS handles RF signal sliding in both thetime and frequency domains, which need to be dealt with given thedistances involved and the relative speeds involved. In general, unlessotherwise indicated, the teachings herein can be applied to one or moreof these examples of multiple access methods and systems, whereinmultiple mobile stations are communicating, or attempting tocommunicate, with a BTS and to avoid interference, the protocols usedprovide for multiple access by having the MSs each use differenttimeslots, carrier frequencies, and/or code sequences. Thus, while manyexamples are described with reference to TDMA/FDMA protocols, theexamples could extend to other protocols.

Herein, distances might be expressed in other than kilometers and inthose cases, certain conversions are assumed. For example, the speed oflight in vacuum might be a conversion factor where distances areexpressed in units of seconds, such as microseconds and milliseconds.The propagation delay in a particular situation might be the speed oflight in vacuum or might be longer, but from context it will be apparentto one skilled in the art how to determine a distance given apropagation delay expressed in units of seconds.

Likewise, distances and/or times might be expressed in units of bits andin those cases, a certain bit rate is assumed. For example, for a bitrate of 270.833 kbit/s, a time period expressed as “156.25 bits” wouldrefer to a time period of 576.92 μs and a distance expressed as 10 bitsmight correspond to a distance of 5.538 km, since transmitting 10 bitswould occupy 36.92 μs, and in those 36.92 μs, the signal could travelthose 5.538 km (round-trip) at the speed of light in vacuum. Thedifferences between the speed of light in vacuum and the actualpropagation speed might differ and that might be taken into account, butfor the purposes of illustration, those details might be omitted so asto not complicate the explanations.

Description of an Example BTS and its Operation

The present invention will be described in detail with reference tospecific, but not necessarily preferred, embodiments of the invention.These specific embodiments are by way of example and one skilled in theart of multiple access communications systems and the art of orbitalmechanics will recognize upon reading this disclosure that othervariations are possible and this disclosure is relevant to many types ofmultiple access communication systems between MSs on the surface of aplanetary body, and spacecraft BTSs operating in a variety of orbitsaround that body.

In many examples herein, the orbit for a satellite including a BTS isgiven as a circular orbit with an altitude of 500 km, but it should beunderstood that the teachings herein apply to other orbits, adjustedaccordingly. In some examples, the BTS operates as, or simulates theoperation of, a GSM BTS or performs enough of the functions tocommunicate with a terrestrial mobile station (MS) that is near thesurface of the Earth, i.e., not in orbit.

In some of the examples herein, the footprint of the satellite is givenas the set of points on the surface of the Earth, or near the surface ofthe Earth for which the satellite is at a minimum elevation angle orgreater as seen from a MS. As used herein, when a satellite is directlyoverhead a MS, the MS “sees” the satellite at an elevation angle of 90degrees (and thus the MS is in the direction of nadir relative to thesatellite). In examples herein, the slant range is from 90 degrees to 40degrees, but other slant ranges might be used that are greater than orless than that. A person of ordinary skill in the art, after readingthis disclosure, would understand how to modify the calculations hereinaccordingly.

Using a radius of 6370 km for the Earth, and assuming a 500 km circularorbit, a MS within the footprint will be 500 km from the BTS when theelevation angle is 90 degrees. Using basic geometry, it can bedetermined that, from a point on the Earth's surface, a satellite in a500 km circular orbit would appear with an elevation of around 40degrees relative to the horizon at that point when the distance from thesatellite to that point is around 741 km. The propagation delay ofsignals between a MS and a satellite BTS is a function of distance anddistance to a satellite in orbit is a function of the orbit radius andthe elevation angle, which is the angle between the position vector ofthe satellite and the position vector of the MS. When the elevationangle is 90 degrees, i.e., the satellite is overhead and the MS is atthe surface point in the direction of the nadir of the satellite, thedistance can be taken as the difference between the orbital radius andthe Earth's radius, or approximately so. When the elevation angle islower than 90 degrees, the distance can be calculated. For some minimumelevation angle at which a connection is expected to be created, it isgenerally considered that angle will correspond to the longest supporteddistance for such connections. With a 40 degree minimum elevation angle,the interaction time between the MS and satellite BTS can be calculatedat the BTS and/or MS as follows. For a 40 degree elevation angle and a500 km circular orbit, the Earth central angle isACOS(R_earth*COS(min_elev)/(R_earth+h))−min_elev=4.74 degrees, whereR_earth=6370 km (the radius of the Earth), min_elev is the minimumelevation angle (40 degrees, in this example), and h is the satellitealtitude (500 km, in this example). The time it takes for the MS to gofrom 40 degrees minimum elevation angle with respect to the satellite onone horizon to 40 degrees minimum elevation angle with respect to thesatellite on the other horizon can be computed as the time it takes thesatellite to traverse 2*4.74=9.47 degrees of the Earth's surface. Asexplained herein, a satellite at 500 km circular orbit is moving at 7.11km/s with respect to the Earth's surface. So the time, in seconds, ittakes to traverse 9.47 degrees of the Earth's surface at this velocityis approximately 9.47 degrees* pi/180*(R_earth+h)/7.11 km/s=159.86seconds. Of course, other minimum elevation angles could be used and thecalculations adjusted accordingly. This assumes that the MS traversesdirectly through the center of the satellite footprint as it passesoverhead. In various states, the BTS and/or MS can take this value of159.86 seconds into account for planning and coordinating communicationsand scheduling.

The actual distances might be different depending on atmospheric effectsand other physical interactions. In this example, the BTS is thenconfigured to support communication with devices that are between around500 km to 741 km between the BTS and the MS and does need to support MSsif those MSs see the BTS at an elevation of lower than 40 degrees from alocal horizon. In some implementations, the lower end is lowered fromthe orbital distance to allow for communications with MSs that are wellabove the ground. For example, if the MS is located in an airplane thatflies at 15,000 meters but the satellite assumes a minimum distance of485 km, then that MS could be supported. In another example, a satellitein Geosynchronous Earth Orbit (GEO) could provide the BTS, in which casethe minimum distance is around 35,786 km.

FIG. 1 illustrates an environment in which the present invention mightbe used. As shown there, on the surface 102 of the Earth (or otherplanetary or celestial body, for that matter) there are several mobilestations (MS) 104 that can be mobile or possibly portable or stationarybut functioning as MSs. These MSs 104 communicate with orbital BTSs 106over BTS-MS links 108. As illustrated, each of the BTSs 106 has anorbital velocity relative to the surface 102, as well as some separationdistance.

FIG. 2 illustrates additional examples for the environment of FIG. 1,wherein persons 202 have various devices 204 that include elements thatconstitute a mobile station, such as a smartphone 204(1), a laptopcomputer 204(2), and a tablet device 204(N), each of which areconfigured and/or adapted to communicate with a terrestrial BTS andwhere persons 202 desire to communicate or access the Internet 208and/or Internet-connected resources 210, they can do so via BTS 206.Other examples of devices might be user interfaceless devices such asindustrial or home equipment that interacts over a network (e.g.,“Internet of Things” devices).

FIG. 3 illustrates an example of a frame-based protocol used between abase transceiver station (BTS) 306 and a mobile station (MS) 304 over aground-to-orbit link 308 using a protocol such as TDMA or other protocolthat might also be used for terrestrial communications.

As will be explained in examples herein, a BTS uses various techniquesthat allow it to transparently support MSs that are merely configuredfor terrestrial cellular communications. Several examples will bedescribed, but first some methods for range extension in a TDMA systemwill be described.

FIG. 4 illustrates how the timing advance mechanism might be used. Asshould be understood, when timing diagrams are shown, it is implied thatthere are corresponding modules with logic that follow the timingdiagram. FIG. 4 also shows effects of propagation delay and the use of atiming advance when using a time-division protocol.

In FIG. 4, eight timeslots of a TDMA frame are shown. These might bepart of a larger data structure, which is omitted for clarity of theexplanation. If a MS or a BTS has an assigned timeslot for MS-BTScommunication, each of the devices are programmed to use their localcopy of a system clock to determine when to start transmitting, when tostop transmitting, when to start listening and when it can stoplistening, which would correspond to their assigned timeslot.

In FIG. 4, the top line illustrates a transmission 402 from an MS.Herein, “Tx” is an abbreviation for transmission, transmitter,transmitting, as the context might require. Similarly, “Rx” is anabbreviation for reception, receiver, receiving, as the context mightrequire. As used herein, a “transmission” is that which is sent as partof a communication or signal from a transmitter and a “reception” isthat which is received. The transmission and its corresponding receptiondo not occur at the same system time where the transmitter and receiverhave the same system time and there is measurable propagation delay.From the perspective of the MS, the process of sending transmission 402occurs entirely within timeslot 1 and here it is assumed that the MS isassigned timeslot 1. Should the transmission 402 take up most of theallotted timeslot, when it is received at the BTS as BTS Rx after apropagation delay, it will be received as reception 404, which isreceived in part during timeslot 2. This is undesirable. With a timingadvance, the MS sends a transmission 412 before timeslot 1 begins (fromthe MS's clock timing) and when it is received at the BTS after apropagation delay as reception 414, it will complete entirely withintimeslot 1 at the BTS.

FIG. 5 shows an example of the use of an extended range feature of atime-division protocol. The duration of a timeslot in this example isaround 0.28 milliseconds, representing a distance of 85 km, so an MS cancommunicate with a BTS without needing any timing advance, as thetransmission can be delayed at the BTS by as much as the duration of onetimeslot. The extra timeslot serves as an additional guard period.

As illustrated in FIG. 5, at a MS, there are eight timeslots, but onlythe first (slot 0), third (slot 2), fifth (slot 4), and seventh (slot 6)are used. As illustrated, MS1 makes a transmission 502(0) duringtimeslot 0, MS2 makes a transmission 502(2) during timeslot 2, MS3 makesa transmission 502(4) during timeslot 4, and MS4 makes a transmission502(6) during timeslot 6. The BTS receives a reception of suchtransmissions, receiving a reception 504(0) starting any time after thestart of timeslot 0 and ending any time before the end of timeslot 1(referred to as “(0)” in the figure). Similarly, the BTS receives areception 504(2) after the start of timeslot 2 and ending any timebefore the end of timeslot 3 (“(2)”), and likewise for receptions 504(4)and 504(6).

FIG. 6 shows an example of the use of an extended range feature of andtiming advance with a time-division protocol. As shown there, the MStransmissions 602 are during their respective timeslots and the BTSreceives such transmissions, receiving receptions 604 at the appropriatetime. With a combination of the timing advance mechanism and theextended range mechanism, the maximum allowed MS-BTS could be 35 km+85km=120 km, as illustrated in FIG. 6. Whether the timing advancemechanism is used alone, the extended range mechanism is used alone, orboth are used, the BTS can manage which ones are used. A MS might noteven be aware of whether the extended range mechanism is being used, asthe BTS would simply not assign every other timeslot. For example, if aBTS determined that a MS was 60 km away, the BTS might tell the MS touse a 0-bit timing advance (i.e., do not use the timing advance) and notassign the next timeslot to any MS. If a BTS determined that a MS was 95km away, the BTS might tell the MS to use an 18-bit timing advance andnot assign the next timeslot to any MS.

FIG. 7 shows an example of a variety of MSs at different distances froma BTS where those distances are determined, at least approximately. Inthis example, there are seven MSs, labelled A through G with respectivepseudo distances between d_(A) through d_(G). This illustrates how MSsmight be sorted by distance.

FIG. 8 illustrates how various MSs at different distances in FIG. 7 areassigned timeslots based on their determined distances to provide forsorted extended range communications. As shown in FIG. 8, timeslot 0 isassigned to user G, which in FIG. 7 is the closest to BTS and timeslot 6is assigned to user E, which in FIG. 7 is the furthest from the BTS.Only seven timeslots are assigned. Given the range of propagationdelays, the transmissions 802 from the various MSs are received asreceptions 804 such that no transmission 802 overlaps anothertransmission 802 and all of the receptions 804 are received within theTDMA frame period. As illustrated in FIG. 8, the signal bursts areincreasingly delayed over timeslots that can eliminate collisions andinterference.

The sorted extended range method has more throughput than the extendedrange mechanism, but still can allow for up to a 120 km range of MS-BTSdistances and ⅞ths of the full frame capacity (so long as there isn'tmore than a whole 85 km distance gap between two sorted MSs). In somecases, more than one timeslot would be allocated to be split up fordistance gaps, and so if N timeslots are so allocated, where N is from 1to 7, the throughput would be 1-(N/8) of the full frame capacity. Wherea timeslot is 156.25 bits, the gaps might be assigned as a number ofbits distributed among the timeslots. As this logic is performed by theBTS, implementation of the sorted extended range mechanism does notrequire any modification to the MS logic or operations because the BTSis orchestrating the calculated timeslot assignments.

FIG. 9 illustrates the distance range of a BTS that uses the ringextended range mechanism and a coverage area for a ring method using asynchronization offset. The cross-hatched area is the area that the BTSsupports. A MS that is closer than the minimum communication distance,d*, is not supported, as the BTS assumes that all MSs are at least d*away. The 35 km range obtained using the timing advance mechanism can beused to support a MS-BTS range from d* to d*+35 km without requiring anyMS modifications. In one example, d*=85 km, but other minimumcommunication distance might be used. In that example, then, the BTScould support an MS that is between 85 km and 120 km from the BTS.

FIG. 10 illustrates the timing of transmission and reception and howtiming is adjusted for the ring method. The minimum communicationdistance, d*, scales directly with the timeslot synchronization offsetselected for use by the BTS on the uplink subchannels. At the MS, atransmission 1002 is sent by the MS in what it sees as timeslot 0. Atthe BTS, a reception 404 is received after a propagation delay that isat least d* times the speed of light. Since the value of d* times thespeed of light is known, the BTS can simply shift the timing of itstimeslots by an offset, T_offset=2×d*/(speed of light), with the 2accounting for the MS-BTS round-trip distance, and the BTS receivesreception 1004 within timeslot 0 at the BTS.

FIG. 11 illustrates an example of a satellite footprint, rings, and theresulting distance ranges for rings of that satellite footprint. Asatellite 1102 would have a coverage footprint that in FIG. 11 isillustrated edge on as footprint 1104 and from above as footprint 1106.The different cross-hatching in footprint 1106 indicates differentdistance ranges between the surface and the BTS, which form rings. Inthis example, there are seven rings, but more or fewer might be present,depending on needs. In this example, the rings are labeled r₀ through r₆and correspond to the BTS-MS distance ranges (which might be pseudodistance ranges) of {500-534.4, 534.4-568.9, 568.9-603.3, 603.3-637.7,637.7-672.1, 672.1-706.6, 706.6-741} (all in km). Each of these rangeshappens to be just less than 35 km, which is a useful design choice asexplained below. Other applications might use different design choices.In an initial handshake, such as a RACH process, a BTS-MS distance isdetermined and from that, an MS can be assigned to one of the rings inthe satellite footprint.

As explained below, MSs assigned to a particular one of the rings mightall be assigned to one carrier frequency or block of carrier frequenciesover which a TDMA/FDMA frame is transmitted, or other approaches mightbe taken. In some embodiments, the rings might overlap such that a MScan be in more than one ring. For example, the first two rings might be490-540 and 530-580, so an MS at 535 km from the BTS can be in either ofthose rings.

Depending on the desired application, an orbital BTS might adjust itsprotocols and operations according to (1) timing advance method, (2) anextended range method (using fewer than all timeslots that are availableand instead using unused timeslots as guard bits), (3) a sorted extendedrange method (using fewer than all timeslots that are available andinstead using unused timeslots as guard bits, allocated betweentimeslots where the timeslots are assigned based on expected variabledelays), (4) a ring extended range method (shifting timing so thatcoverage is a ring with an inner circle that is not supported), (5) amulti-ring extended range method (like method (4) with multiple rings tocover different ranges of distances at the same time and MSs assigned toa ring based on its BTS-MS distance) and (6) a sorted channel-ringallocation method (like method (5) and with different rings associatedwith different carrier frequencies and, for a carrier frequency, method(3) is used for the MSs within that ring's distance range to allocatetimeslots), or a combination of one or more of (1), (2), (3), (4), (5)and (6).

Timing Advance, Ring and Sorted Extended Range Methods

FIG. 12 illustrates a first example, of a BTS using a timing advancemethod, a ring extended range method and a sorted extended range method.There, different mobile stations might be assigned different timeslotsbased on their terrestrial location to implement a sorted extended rangemethod for TDMA communications and the ring method is used to get therange to be terrestrial.

In this example, a satellite 1202 is orbiting at an altitude of d* andit is assumed that the satellite 1202 does not need to support an MSthat is closer than d* and does not need to support an MS that isfurther from some maximum distance, d_(max), from the BTS. In thisexample, there are five MSs, MS1 through MS5, labeled by distance fromthe BTS, that are between d* and d_(max). The MSs MS1 to MS5 areassigned to timeslots 4 through 0 respectively, with timeslots 5, 6 and7 unallocated, so that the sorted extended range method can be used withthree timeslots worth of guard time. This corresponds to around 486 bitsand is illustrated in the MS frame 1204. As a result of the distancesbetween MS and BTS, the signal bursts from MS1 through MS5 are receivedas indicated in the BTS frame 1206 shown.

In this example, the timing advance is 22 bits (needed for 12 km ofrange) and the synchronization offset for the ring is 875 bits, whichcorresponds with a distance of around 488 km, so d* is around 488+12=500km. The extended range guard time uses up three timeslots, but thatprovides for a full range of MS-BTS distances (i.e., d_(max)−d*) ofaround 295 km. Assuming up to 35 km of range for the timing advance,which could be from 0 to 63 bits, the sorted extended range method rangecan be from around 35 km to around 640 km depending on how manytimeslots are allocated to guard time, as shown in Table 1. In Table 1,the ranges assume that the full range of 0 to 63 bits of timing advanceis available.

TABLE 1 # of Extended Guard Timeslots Range (i.e., d_(max) − d*) (in km)0 ~35 1 121.34 2 207.82 3 294.29 4 380.76 5 467.24 6 553.72 7 640.19

This TDMA frame structure allows for satellite-based cellular coverageof a large geographic area. Even with this solution, there are stilloperational problems and challenges that need solving. Firstly, eachframe has just over one-half of the throughput potential of a typicalGSM frame. Secondly, in this configuration, each frame will be subjectto a variable Doppler shift of between plus or minus ˜35 kHz (which willvary from solution to solution depending on orbit selection, slantrange, frequency use, etc.). The Doppler shift issue can be mitigated,however, using the on-orbit BTS methods and apparatus described herein.The timing challenge might be solved with the next method.

Timing Advance and Sorted Channel-Ring Allocation Methods

FIG. 13 illustrates how different mobile stations might be assigneddifferent channels based on their terrestrial location relative to theBTS so that the ring method can be used with varying ring diameters fordifferent channels. As shown there, a method that uses timing advance(for a ˜0 to 35 km range) and a sorted channel-ring allocation methodcan provide around another 241 km of range without using up timeslots.With the sorted channel-ring allocation method, the satellite footprintis divided up into rings as illustrated in FIG. 11 and each ring ispaired with a distinct carrier frequency. Each ring operates with adifferent synchronization offset.

As used herein, a channel might comprise one or more specific frequencydivisions in a protocol, such as a group of carrier frequencies. In FIG.13, the range of supported pseudo distances between the nearest andfarthest potential targets is 241 km, partitioned into seven pseudodistance range rings. This results in coverage ranges of around 34 kmper ring and the synchronization offsets can be different for differentrings assigned to channel blocks, or sets of channels. By having theoffsets from channel block to channel block be less than around 35 km,full throughput is possible in each channel by eliminating the need forextra slot guard periods and then timing advance by itself issufficient.

RACH request bursts can be used to determine the propagation distancefrom each MS's signal. The BTS can use the broadcast channel (BCCH) toconstantly or periodically notify MSs on the RACH as to which carrierfrequency and timeslot the BTS assigns to that MS for use to uplink. TheBTS would know exactly when the MS will transmit its RACH burst and cancount the number of bits between that time and when the actual burstarrives. By dividing that number of bits by the channel bit rate (270.83kbps for GSM), the BTS can calculate the round-trip propagation delaytime. The BTS then calculates the propagation distance, or pseudodistance, by dividing the speed of light by the round-trip propagationdelay time. Depending on the calculated pseudo distance, each MSqualifies for an assignment to a channel in a particular channel block.For instance, in the configuration shown in FIG. 13, channels in channelblock b₀ are assigned to MSs that have calculated pseudo distancesbetween 500 km and ˜534 km; channels in channel block b₁ are assigned toMSs that have pseudo distances measured between ˜534 km and ˜568 km fromthe on-orbit BTS, and similarly for other ranges as shown in FIG. 11 andFIG. 13.

The first channel block, b₀, has uplink TDMA frames that are offset fromthe transmit uplink frames by the same amount as shown in FIG. 12. Thefollowing channel block, b₁, has frames that are offset by an additional˜62 bits from the frame of channel block b₀. Each channel block's framethereafter has ˜62 bits in additional offset compared to the previouschannel block (i.e., the frame of channel block b_(i+1) is offset anextra ˜62 bits from the frame of channel block b_(i)). Thisconfiguration, leveraging 62 bits, creates the various coverage rings,each ˜34 km, as each bit of frame offset corresponds to around 555 m,and each ring/channel block is extended ˜34 km further than the priorone. By assigning various synchronization offsets, each channel blockexhibits coverage of a different ring in space (and on the surface ofthe Earth). When the channel blocks are given synchronization offsets inincrements of 62 bits and the classic embodiment of GSM is used, fullthroughput can be achieved on every channel, and vastly expansivecoverage can be accomplished. This can be done without requiringmodification of a GSM MS. A top-down view of the range rings is shown inFIG. 11. Each range ring's channel block is defined by a distinctive“range of distances” which is prescribed for this particular embodimentin the key to the left in FIG. 11.

Doppler Shift Handling

While the above methods and their variations can provide maximumthroughput for all channeled spectrum, the frequencies of transmissionsmight be different on transmission and reception due to relativemovement of the BTS and the MSs. A Doppler solution can be used toaccount for scenarios in which multiple MS may exist within similarpseudo distance ranges from the on-orbit BTS but experience widevariance in perceived carrier frequency shift. For instance, considertwo MS that are calculated to exist within the same ring/channel block,b₆, in FIG. 11, where one MS is positioned at the top forward tip of thesatellite coverage footprint while the other is positioned at the bottomtip of the satellite coverage footprint.

In FIG. 11, the satellite is directly above the center of the coveragearea indicated for channel block b₀ (at the origin of the arrow) and ismoving in the direction of the arrow labeled “velocity”. A first MS infront of the satellite velocity vector will experience a positiveDoppler shift in received frequency, while a second MS behind thesatellite velocity vector will experience a negative Doppler shift inreceived frequency. If these MSs are assigned the same frequency, thesatellite could receive signal burst frequencies from the MSs that aremany kilohertz apart (up to 70 kHz apart, in the case of 1800/1900 GSMband). Furthermore, assigning adjacent channels to MSs that experiencewidely different Doppler shift environments could result in signalinterference at the satellite.

FIG. 14 shows how a satellite footprint might be subdivided into Dopplershift strips for methods of mitigating this issue. As illustrated there,assume a satellite 1402 traveling with a velocity relative to thesurface 1404 of the Earth. The satellite footprint 1406 is a view fromthe satellite with the velocity as indicated. A MS in area 1410 of thesatellite footprint 1406 vector will experience a positive Doppler shiftin received frequency of signals from satellite 1402, whereas a MS inarea 1412 of the satellite footprint 1406 vector will experience anegative Doppler shift in received frequency of signals from satellite1402. The specific Doppler shift in received frequency can be determinedusing simple geometry, and for ranges of Doppler shifts, the satellitefootprint 1406 might be divided into strips delimited by the contourlines and the contour lines assigned values 1420 for their respectiveDoppler shifts.

In three-dimensional space, the Doppler shift at any point within thesatellite footprint can be calculated by the BTS or the MS, givensufficient information. One method of doing so might assume all vectorsare represented in the Earth-Centered, Earth-Fixed (ECEF) coordinateframe. This is also known as Earth's rotating frame because it is thecoordinate system that rotates in space with the Earth around its axisof rotation). In this process, each of the vectors are treated as vectorquantities with three component values, such that each component valuein the vector represents a value along each dimension of the coordinateframe represented by the vector. Such numbers can be stored in memoryfor a processor to manipulate.

If r _(BTS) represents the position vector of the satellite in ECEFcoordinates and r _(MS) represents the position vector of the MS in ECEFcoordinates, then the position vector of the MS with respect to the BTSwould be r _(MS/BTS)=r _(MS)−r _(BTS). Similarly, if v _(BTS) representsthe velocity vector of the satellite in ECEF coordinates and v _(MS)represents the velocity vector of the MS in ECEF coordinates, then thevelocity vector of the BTS with respect to the MS is v _(BTS/MS)=v_(BTS)−v _(MS). To calculate the Doppler shift, the magnitude of thecomponent of the BTS's velocity with respect to the MS, v _(BTS/MS), inthe direction, or unit-vector, of the position of the MS with respect tothe BTS, r _(MS/BTS)/∥r _(MS/BTS)∥, a processor computes this positionand then divides by the wavelength of the assigned carrier frequencywave. This can be done using the dot product of the two vectors ofinterest, v _(BTS/MS) and r _(MS/BTS)/∥r _(MS/BTS)∥, and can be writtenas in Equation 1 and perhaps implemented in program code.

$\begin{matrix}{D = {\left\lbrack {v_{{BTS}/{MS}} \cdot \frac{r_{{MS}/{BTS}}}{r_{{MS}/{BTS}}}} \right\rbrack*\frac{1}{\lambda}}} & \left( {{Eqn}.\mspace{14mu} 1} \right)\end{matrix}$

In Equation 1, D is the computed Doppler shift and λ is the wavelengthof the carrier frequency wave, which can be computed as the carrierfrequency divided by the speed of light.

By way of example, consider a spacecraft operating in an equatorialorbit at an altitude of 500 km and happens to be right above the primemeridian at a particular instant (e.g., directly nadir relative to thesatellite is the intersection of the equator and the prime meridian). Atthe same particular instant, a stationary MS 1430 is positionedapproximately at sea level below the spacecraft but rests on the equatorat 1 degree east longitude (e.g., latitude longitude position can bedescribed as [0, 1]).

In this scenario, the ECEF position coordinate of the satellite isapproximately [6870 km; 0 km; 0 km]. The velocity vector of a spacecraftin a circular orbit at 500 km is approximately perpendicular to theposition vector and parallel with the equator (for equatorial orbit).The magnitude of the velocity vector with respect to the Earth's surfacecan be calculated as SQRT(mu_earth/(R_e+h))−w_earth*(R_e+h)=7.11 km/s,where mu_earth is the Earth's gravitational constant(mu_earth=398658.366 km³/s²), R_e is the radius of the Earth at theequator (R_e˜6370 km), w_earth is the angular velocity of the Earth'srotation (w_earth=7.27*10⁻⁵ radians/second), and h is the altitude ofthe satellite (h=500 km in this example). The ECEF velocity vector ofthe spacecraft is therefore approximately [0 km/s; 7.11 km/s; 0 km/s].The ECEF position of the stationary MS at 0 degrees latitude and 1degree east longitude is approximately [R_earth*cos(1°);R_earth*sin(1°); 0]=[6369 km; 111 km; 0]. The ECEF position of thisstationary MS with respect to the spacecraft is therefore, [6369 km; 111km; 0]−[6870 km; 0 km; 0 km]=[−501 km; 111 km; 0]. The Doppler shift ofa 1900 MHz signal received by this MS from the spacecraft will thereforebe as shown in Equations 2, 3 and 4.

$\begin{matrix}{D = {\left\lbrack {v_{{BTS}/{MS}} \cdot \frac{r_{{MS}/{BTS}}}{r_{{MS}/{BTS}}}} \right\rbrack*\frac{1}{\lambda}}} & \left( {{Eqn}.\mspace{14mu} 2} \right) \\{D = {\left\lbrack {\left\lbrack {0;{7.11\mspace{14mu}\frac{km}{s}};0} \right\rbrack \cdot \frac{\left\lbrack {{{- 501}\mspace{14mu}{km}};{111\mspace{14mu}{km}};0} \right\rbrack}{513.149\mspace{14mu}{km}}} \right\rbrack*\frac{1}{0.158\mspace{14mu} m}}} & \left( {{Eqn}.\mspace{14mu} 3} \right) \\{D = {9.734\mspace{14mu}{kHz}}} & \left( {{Eqn}.\mspace{14mu} 4} \right)\end{matrix}$

As explained above, the signal received from a MS on the RACH at the BTScan be used to calculate the pseudo distance. It can also be used toapproximate the Doppler shift from the MS. Much like the BTS knows whattimeslot the RACH is on, it also knows what carrier frequency it is on.So, when the BTS receives the RACH burst, it can measure the center ofthe burst frequency and calculate its offset (difference) from theexpected center frequency on the RACH. This may or may not require thesatellite BTS to listen on a wider frequency range on the RACH dependingon what magnitude of Doppler shift the system experiences.

FIG. 15 is a flowchart of a measurement process, which might use RACH,for a BTS to determine a pseudo distance and a Doppler shift from a MS.A RACH might be indicated when a MS wants to initiate a session (e.g.,send an SMS text, make phone call, send data). The Doppler shift valuedoes not need to be measured/updated often. The Doppler shift valuechanges over the time it takes to request access to the channel and sendthe data payload are typically not large enough to be damaging to thesystem's ability to send/receive the signals. In cases where that mightbe an issue, the BTS can make predictive changes and assume the MS isn'tmoving very fast. This process can be used for the satellite BTS inmanaging the measurement of pseudo distances and Doppler shifts tocoordinate channel assignment/allotment.

As illustrated in the flowchart of FIG. 15, at the start of the process,a satellite BTS broadcasts RACH timing information on the BCCH channel(step 1501) and then a MS learns which timeslot the RACH is on (step1502). Knowing that, the MS sends a burst during the RACH timeslot thatthe BTS instructed the MS to use (step 1503). The burst arrives at theBTS both late and offset in frequency (step 1504). The BTS flow then hastwo threads, one for delay and one for Doppler shift. In the first flow,the BTS counts the number of bits the burst was delayed by (step 1505),divides the number of bits counted by the channel bit rate to computethe round-trip delay (step 1506), and then divides the round-trip delayby twice the speed of light to compute the pseudo distance (step 1507).In the second flow, the BTS measures the center frequency of the burst(step 1508), and subtracts the center frequency from the centerfrequency of the RACH to compute the Doppler shift (step 1509). The twothreads then combine and the BTS checks the channel configuration matrixto assign the MS a channel configured for its pseudo distance and itsDoppler shift (step 1510). The BTS then checks whether a channel isalready configured (step 1511). If yes, the BTS assigns the MS theconfigured channel (step 1513) and if no, the BTS configures a channelfor the MS pseudo distance and Doppler shift environment detected (step1512), and the process ends.

Since the BTS can acquire knowledge of the Doppler shift from each MS,it can assign specific Doppler shift ranges to specific channels. Indoing this, each individual channel can have its own specific andlocally reduced range of potential Doppler shift values. For instance,some channels may only ever experience 0 to 5 kHz shift in carrierfrequency, while others will only ever experience 25-30 kHz shift incarrier frequency, as the channels are assigned to MSs in specificstrips shown in FIG. 14. Since the Doppler range is clearly defined andmore localized for each channel, it can be used as a qualifier forchannel allocation and assignment. This method makes it much simpler tohandle wide Doppler shift variances across the entire set of serviceableMSs within the satellite footprint.

Referring back to FIG. 14, that figure illustrates the perceived Dopplershift at various locations across the satellite coverage footprint.Intuitively, half of the satellite footprint in direction of thevelocity vector will experience a positive Doppler shift while the otherhalf will experience negative Doppler shift. What is less intuitive isthat the geometry of the curvature of the earth creates a Doppler shiftmap in the satellite footprint that is described by increasingly curvedcontour lines.

One approach, as described herein, is to allocate channel blocks intopre-determined Doppler shift blocks, much like the channel blocks areallocated into pre-determined pseudo distance range rings, as describedabove. If the carrier frequencies are assigned to specific pseudodistance ranges and Doppler shifts, the actual Doppler shift experiencedon each channel will be unique to that channel's frequency.Implementations of this method would account for this. In one design,the contour map for Doppler shifts uses the center frequency for thespectrum in discussion and in the figure, GSM at 1900 MHS with a 500 kmaltitude satellite and 40 degree elevation angle is assumed.

In FIG. 14, each dashed line defines a border for a Doppler shift stripthat is used to localize the potential Doppler shift for each channeland, therefore, minimize interference. The curvatures of the contourlines on the map are a result of the geometry of the communication linkas well as the frequency of communication.

FIG. 16 shows how a satellite footprint might be subdivided into rangerings, into Doppler shift strips, and into both range rings and Dopplershift strips. As illustrated, the ranges of pseudo distances form ringsand the Doppler shift contours form strips. Overlaying these into a grid(not necessarily an orthogonal or linear grid), a satellite footprint1602 is divided into grid cells bounded by a first distance value, asecond distance value, a first Doppler shift value and a second Dopplershift value. Each of these grid cells corresponds, therefore, to acombination of a range of pseudo distances and a range of Doppler shiftsrelative to the on-orbit BTS and is the qualifier for a MS to beassigned a particular channel (or one within a set of particularchannels).

It should be noted that while the satellite footprint represented hereis circular in nature, that is not required. The footprint could be moresquare or elliptical in shape depending on which antennas are used onthe satellite and how they are configured. A non-circular footprintmight provide advantages in that it can increase or decrease the spreadof propagation delays and/or Doppler shift environments within thefootprint.

This grid represents the combinations of ranges of pseudo distances andranges of Doppler shifts that correspond to the qualifications for thepseudo distance and Doppler shift channel blocks. The grids cellsdescribed above are assumed symmetric about the satellite velocityvector. This means that each grid cell that is off of the centerline ofthe satellite coverage area has a “twin” grid cell on the opposite sideof the satellite footprint. The term “twin” grid cell is used becausethese two grid cells share a “bucket” that is logically associated witha range of pseudo distances and a range of Doppler shifts (i.e., an MSis logically assigned to a bucket based on whether the MS's pseudodistance is within the range of pseudo distances assigned to that bucketand the MS's Doppler shift is within the range of Doppler shiftsassigned to that bucket), since MSs in both of these grid cells operateat similar pseudo distances and Doppler shifts.

Handling Doppler Shifts of Certain MS Devices

Some protocols might be more resilient to Doppler shifts whendemodulating a downlink signal, while others might be less so. In somedevices, or some protocols, a shift of 2.5 kHz might be the Dopplershift threshold. However, even some low-end cellular telephones might beable to demodulate the BCCH signal with up to a 20 kHz offset from whatwould typically be that channel's center carrier frequency. This mayrelate to an interaction between the BTS and the MS on the FCCH(Frequency correction channel), which is another broadcast channel thatthe MS uses to synchronize its local clock with the BTS. Thissynchronization is ultimately the information the phone needs to thendemodulate the BCCH and other downlink channels. Thus, Doppler shiftstrips larger than the exemplary 5 kHz strips used in an example abovemight be used. For example, the buckets might be adjusted and stretchedto accommodate larger ranges of Doppler shifts, up to at least 20 kHz ineither direction. In effect, this can obviate the need for Doppler shiftbucketing when the satellite footprint is small enough that the highestDoppler shift case is less than 20 kHz. This might not be true for otherprotocols, such as NB-IoT, which use much smaller signal bandwidths.NB-IoT also has other differences, such as the case where themultiple-access protocol is an LTE NB-IoT protocol and the limiteddistance is 40 km, which would be exceeded by the base-to-mobiledistance.

Channel Assignment

As explained herein, a BTS can support multiple transceivers each usingtheir own carrier frequency that can in turn each support up to eightMSs. A channel can be associated with a transceiver as the transceivercan be set to use one of many possible carrier frequencies. In anexample above, there are 123 available carrier frequencies. Of thosemany carrier frequencies, they can be assigned to MSs as needed, butsome advantages might be had if they are allocated by grid cell, so thatbuckets of similarly situated MSs having similar distances from the BTSand similar Doppler shifts use the same carrier frequency and thecarrier frequencies can be strategically assigned. A channel (whichmight logically comprise an uplink subchannel and a downlink subchannel,as explained above), can be assigned one of the plurality of timeslotsand one of the plurality of carrier frequencies. A channel might beidentified solely by its assigned characteristics, such as its carrierfrequency and its timeslot, but for some situations, each channel isgiven a channel label. A channel's label might encode the channel'scarrier frequency, its timeslot, and possibly its timing advance, andDoppler shift, but it could be that the labels are simpler, such assequential numbers, and the BTS and/or MS include a stored mapping ofchannel number labels to assigned characteristics (e.g., channel 1 usescarrier frequency f₁ and timeslot 0, channel 2 uses carrier frequency f₇and timeslot 3, etc.).

FIG. 17 illustrates one example of range ring/Doppler shift cells of asatellite footprint. The intersection of the pseudo distance rings andthe Doppler shift strips form a footprint grid. The grid cells, rangering/Doppler shift cells, can be assigned channels.

FIG. 18 illustrates an example assignment of the range ring/Dopplershift cells of FIG. 17 to particular carrier frequencies and Doppleroffset blocks. The logical channel blocks can be associated with one ormore carrier frequencies and/or timeslots on the TDMA frames using thosecarrier frequencies. In FIG. 17, channels are shown with arbitrarychannel labels, in this case from 1 to 70. They happen to be in labeledin order from bottom to top, i.e., from most negative Doppler shift tomost positive Doppler shift. The channels 1 to 70 might correspond tochannels assigned to each of eight timeslots in frames that use eightcarrier frequencies and six timeslots in a frame for one more carrierfrequency.

The diagram of FIG. 17 shows how the grid cells of the satellitefootprint are assigned channel numbers. Only the left side of thefootprint is shown numbered, but it should be understood that the twincells on the right are also assigned to those channel numbers. Thechannel allocation table in FIG. 18 illustrates a channel allocationscheme in which each channel number is associated with, allocated orassigned a Doppler offset block corresponding to a Doppler shift strip(from D₀ to D₁₃) and a channel block (from b₀ to b₆). Note that in otherembodiments, the number of channels might change with the decision forhow to “bucket” pseudo distances and Doppler shifts for MSs. Multiplechannels can be assigned to a grid cell. In the example of FIGS. 17 and18, one channel number is assigned per grid cell for simplicity. Onlyhalf of the grid cell is filled out with channel assignments because itis symmetric about the satellite velocity vector. The grid cells thatare not filled in, in an actual implementation, are assigned the samechannel number in the grid cell on the opposite side relative to it inthe contour map. This is because although the symmetric grid cells existin different physical locations on the contour map (and in the realworld), they represent the same qualification parameters in terms ofpseudo distance from the on-orbit BTS and Doppler shift.

Pinching and Fraying

A “pinching and fraying” feature of the BTS design is useful when theuplink subchannels exist in contiguous spectrum and downlink subchannelsexist in contiguous spectrum and when the Doppler shifts can equal orexceed the signal bandwidth, but these do not have to be the case inorder to implement the following technique.

The table in FIG. 18 is the channel assignment matrix that the on-orbitBTS would use to determine how to assign channels to a MS and wouldassign them in a manner where adjacent numbers are assigned adjacentcarrier frequencies. When a signal burst is received on the RACH, thecalculated Doppler Shift and calculated pseudo distance estimates areused to determine which channel should be assigned to that MS by findingthe appropriate grid cell and looking up the channel number for the MSfrom the table. In this example, not every channel block (the columns inFIG. 18) has the same number of actual channels in use or availablebecause not every channel block corresponds to pseudo distances thatcould experience a full range of Doppler Shift. The BTS stores a copy ofthis table and might have different versions of this table, for use whenassigning a channel number based on grid cell.

Benefits of a channel assignment wherein the channels are assigned inorder of grid cells having particular Doppler shifts are illustrated inFIG. 19. Since the spacecraft is actively assigning channels based onexpected Doppler shift, it no longer needs to account for such a widerange of shift in received frequency. Instead, the on-orbit BTS cancommand the existing MS infrastructure to communicate on a certaincarrier frequency, but will listen on a slightly shifted carrierfrequency depending on how much Doppler shift is expected on thatchannel. This reduces adjacent carrier frequency interference at thespacecraft segment.

In this particular embodiment, the Doppler shift contours are spacedevery 5 kHz, but other spacing might be used. For each channel that isassigned to a MS, therefore, the satellite BTS will listen on a carrierfrequency that is the average of the maximum and minimum Doppler shiftsfor the carrier frequency of that channel and check for a data burst inthe timeslot assigned to that channel. For instance, assume channel 70has been assigned to a MS and is logically associated with a frequencyF₇₀ and a timeslot TS₇₀. The BTS on the spacecraft would listen for anuplink signal from the MS at a carrier frequency of TS₇₀+27.5 kHz. Thisway, no signal is more than 2.5 kHz offset from the frequency beinglistened to by the BTS. In the return link, the on-orbit BTS cantransmit a signal on channel 70 by transmitting its burst at TS₇₀−27.5kHz so that the signal is received at the MS within a reasonable limitof the carrier frequency that it is listening on.

FIG. 19 depicts a map of the uplink and downlink carrier frequenciesthat the MS and BTS use to communicate. Specifically, FIG. 19 shows theDoppler blocks referenced in FIGS. 17 and 18, which have widths that arescaled, based on the number of channels that they hold. When thechannels are assigned as a function of some known Doppler effect and inorder of increasing carrier frequency, the uplink signals “fray” awayfrom each other and define the channels that the BTS chooses to listenon. This mitigates interference at the on-orbit BTS. The downlinktransmit frequencies are “pinched” instead of “frayed” to ensure thesignal has the appropriate carrier frequency when it arrives at the MS.Note that the Doppler blocks are referenced in both the uplink anddownlink frequencies, which implies that each channel has an uplink anddownlink component. Other variations are possible.

FIG. 19 shows that the BTS on-orbit listens at slightly frayedfrequencies relative to the frequencies transmitted by the MS. This is aresult of the novel channel allocation scheme and reduces interferenceand complexity of Doppler shift when communicating with MSs. In downlinkoperations, the spacecraft transmits on more “pinched” channels so thatthe arriving signals at the target MS are the correct frequency. Thechannel blocks are represented as the Doppler blocks referenced in FIGS.17 and 18 and have widths that are scaled by the number of channels theyhold.

It will be noted that the channels could be allotted to Doppler blocksin decreasing order of signal frequency, as well. This method wouldreverse the effects of the received and transmitted signals from the BTSperspective. It is reasonable to assume that this technique mightactually help enhance the ability to close the uplink signal from theMS. This is because the uplink signals would be “pinched” instead of“frayed” like they are shown in FIG. 19. Since the amount of “pinch” isfairly well understood, the on-orbit BTS would leverage this fact tointelligently narrow the bandwidth that “it listens on” for each uplinkchannel. This would mean that the received uplink signals are separatedby less than 200 kHz (as it is in GSM). In this case, the on-orbit BTScould, in theory, listen on narrower channels, to reduce noise.

Some embodiment of the invention might favor “frayed” or “pinched”channels at the BTS on both the uplink and downlink subchannels. Tocater to this, the implementer would assign channels that haveincreasing uplink signal frequencies and have decreasing downlink signalfrequencies. This would result in “frayed” channels for the BTS uplinkreceive and downlink transmit functions. The reverse, channels withdecreasing uplink signal frequencies and increasing downlink signalfrequencies, would result in “pinched” channels for the BTS uplinkreceive and downlink transmit functions.

While FIG. 19 illustrates channels as boxes, one per Doppler block, itshould be understood that a box in FIG. 19 that is frayed or pinched cancorrespond to one or more carrier frequency and one or more timeslot.For example, in the example of Doppler block D₉, FIG. 18 shows thatchannels 50 through 56 are assigned to cells in the strip covered bythat Doppler block. Channels 50 through 56 might represent seventimeslots in frames of one carrier frequency, one timeslot in frames ofseven different carrier frequencies, or some other configuration.

Location Finding

In addition to data communication between a BTS and an MS, the BTS canbe used for location finding, i.e., determining a geographic location ofthe MS, at least approximately or with sufficient resolution for varioususes (supporting remote search and rescue operations, for instance).When a satellite passes over a MS, the BTS of that satellite determines(as explained above) a grid cell for the MS (actually a pair of twingrid cells). When another satellite passes over the same MS, the BTS ofthat second satellite will determine a pair of grid cells in that secondsatellite's footprint. If the second satellite is in a different orbitthan the first satellite, the symmetry lines for its pseudo distancerange ring and Doppler shift contour strip will be somewhat differentthan that of the first satellite. The BTSs assume that the MS has notmoved, or has only moved slightly, on the scale of the satellitefootprints and where the two pair of grid cells are such that one gridcell for a satellite overlaps one grid cell for the other satellite, andthe other two grid cells don't overlap, from that a BTS can determine alikely location of the MS.

This can be used alone or in combination with other location-findingsystems.

Software-Defined Radio; Dynamic Allocation by Density

The BTS performs various functions as described herein. The BTS might beimplemented with commodity software-defined radios, programmed orconfigured with the particular functionality provided herein. Asoftware-defined radio could be reprogrammed in orbit to shift aroundthe channel configuration in the BTS channel allocation scheme. Thiswould be valuable when the MSs on the ground are not evenly distributed.For instance, if the BTS has a mapping of connected MSs, or a mapping ofanticipated MSs, as illustrated in in FIG. 20, or where the BTS isgetting a large majority of its requests from MSs that are exhibitingparticular Doppler shift ranges and are operating within similar pseudodistances, the BTS can favor the more crowded grid cells with morechannels. Thus, the Doppler shift and pseudo range data can be used toprorate channel allocation. The right side of FIG. 20 is a diagramshowing, for each grid cell, how many channels might be allocated tothat grid cell. Only one half circle is shown, with the assumption thatthe satellite footprint is symmetrical about a velocity vector of thesatellite.

FIG. 21 illustrates an example channel allocation table that might beused for the allocation and mapping illustrated in FIG. 20, with channelallotment mapped with ordered channels in a channel allocation scheme.To reconfigure a channel to service a grid cell, the transceiver for thechannel is reconfigured with a different timeslot synchronization offsetfrom the transmit TDMA frames and the transceiver gets an update to itsconfigured frequency offsets for receiving and transmitting on uplinkand downlink carriers, respectively. When the channels are reconfiguredand remapped to the channel allocation scheme, they can remain in order(increasing or decreasing) counting from the bottom right corner of tothe top left corner of the channel allocation table as shown. Thechannel allocation table might be stored in computer-readable memoryaccessible such that a processor that controls a software-defined radiocan set frequencies and timing according to the channel allocationtable.

In addition to remapping channels to blocks, an on-orbit softwaredefined radio could also reconfigure its block mapping. For instance, ifMSs were densely packed, the BTS could reconfigure its channelallocation scheme in more refined intervals of pseudo distance andDoppler shift to improve its service, particularly throughput, forspecific geographic areas. Furthermore, the on-orbit BTS could setminimum and maximum timeslot synchronization offsets and Dopplercompensation for its channels based on minimum and maximum pseudodistance and Doppler shift measurements, respectively. This allows theBTS to more granularly define the grid cell of its satellite footprintand more effectively assign channels to service higher density pocketsof MSs. A more refined interval for Doppler blocks further reduceseffect of Doppler shift on each channel while a more refined intervalfor pseudo distance range rings increases potential throughput in morespecific ring locations to service more densely packed MSs.

On-board processing could also leverage known satellite velocity topredict the motion of the satellite footprint, and therefore, the pseudodistance and Doppler shift contours, relative to the MSs that itservices. This would allow the satellite BTS to predict which pseudodistance and Doppler shift buckets will require channel allotment in thenear future and which will not; predictability would enable more preciseexecution of channel allotment scheme reconfigurations. Since there willbe some lead time associated with channel reconfiguration,predictability could be powerfully leveraged to ensure limited down timefor its channels. For instance, to account for this channelreconfiguration lead time, the on-orbit BTS could “juggle”, or reserve,one or more channels such that the carrier frequencies that areservicing MSs do not need to abruptly stop service in order to bereconfigured. Since channels must be configured in order of increasingor decreasing frequency, reconfiguration can sometimes create a dominoeffect and require many channels to be reconfigured to maintain thiscritical frequency ordering in the channel allocation scheme. Forinstance, consider a GSM BTS on-orbit with access to 80 channels in theGSM spectrum. Assuming the channels are labeled 1 to 124, every oddchannel (i.e., 1, 3, 5, 7, etc.) could be configured to service MSswhile every even channel (i.e., 2, 4, 6, 8, etc.) could be “juggled”, orreserved. When the need emerges for reconfiguration, the on-orbit BTScan reconfigure a “juggled” channel and does not need to disrupt serviceon one of its other 62 already configured channels. When a configuredchannel is no longer servicing MSs, it can be cycled into the reserved,or “juggled”, channel set and the process repeats itself maintainingconsistent service and limiting channel down time.

The on-orbit BTS can be programmed to use real-time measurements ofpseudo distance, Doppler shift, and other data (i.e., GPS) of the MSs tofurther enhance the quality of service of such a network. Examplesinclude re-allocation or shifting of the channels based on large datasets gathered over time and many satellite passes (based on relativelystatic locations of MSs) and more dynamic real-time shifting based onchanges in MS distributions that have been sensed by the spacecraft thatpassed over this location just prior to the present spacecraft, or evenby the present spacecraft.

The dynamic channel allocation described above could also be done in away that allows a particular channel to be dedicated to a particular MS,or geographic location, for the entirety of the satellite overpass. Inother words, a certain channel's Doppler shift and pseudo distanceconfiguration, if plotted over time, would be described by some smoothfunction that matches the Doppler shift and pseudo distance environmentexperienced by a certain MS, or geographical location, over the courseof an overpass. This embodiment could be strategic under conditions whena certain MS on the ground needs to maintain or benefits from a lockedlink with the satellite for a longer period of time (e.g., minutesinstead of seconds).

Consider the case illustrated in FIG. 20 where the connected MSs areoperating in a “clump”—perhaps a remote village. As a reminder, the mapshows only half of a satellite footprint because the pseudo distance andDoppler shift buckets are symmetric about the satellite velocity vector.When the spacecraft gathers the pseudo distance and Doppler shift datafrom these users, it could strategically prorate channel allotment inits channel allocation scheme and reprogram its channels to shift theirservice configuration based on this proration. A technique like thiscould also leverage predictive data analytics software. The on-orbit BTScould marry historic MS data with GPS navigation data to predict whereand when it will come across dense pockets of customers in itsfootprint. GPS data from MSs that are actually serviced could also beused to further enhance predictive analytics and allocation of channels,and tracking applications. This could drive an increase in the qualityof service for such a network.

FIG. 22 illustrates a process for determining parameters for a MS in aRACH process. By measuring propagation delays from MS uplink bursts, aBTS can calculate the required timing advance for each MS to transmitbursts at the correct time. A RACH process might be that (1) the MSlistens to the BCCH as it camps on a BTS, (2) the user of the MS types atext message and hits “send,” (3) the MS, using the information providedon the BCCH, requests access to a channel by sending a burst on theRACH, (4) the BTS looks up the channel assignment and responds with achannel assignment as well as a timing advance (in bits), and (5) the MSuses the timing advance to advance its bursts relative to the time slotthat it has been assigned and uses the frequency carrier it wasassigned.

In the more general case, illustrated in FIG. 22, an MS requests for theallocation of a dedicated signaling channel to perform the call setup,and after allocation of a signaling channel, the request for MOC callsetup, included the TMSI (IMSI) and the last LAI, is forwarded to theVLR. The VLR requests the AC via HLR for Triples (if necessary). Then,the VLR initiates Authentication, Cipher start, IMEI check (optional)and TMSI Re-allocation (optional). If all of this did not cause an errorrequiring cancellation of the process, the MS sends the Setupinformation (number of requested subscriber and detailed servicedescription) to the MSC and the MSC requests the VLR to check (from thesubscriber data) whether the requested service and number can be handled(or if there are restrictions that do not allow further proceeding ofthe call setup).

If the VLR indicates that the call should be handled, the MSC commandsthe BSC to assign a traffic channel to the MS and the BSC assigns aTraffic Channel TCH to the MS. The MSC then sets up the connection torequested number (called party).

According to one embodiment, the techniques described herein areimplemented by one or generalized computing systems programmed toperform the techniques pursuant to program instructions in firmware,memory, other storage, or a combination. Special-purpose computingdevices may be used, such as desktop computer systems, portable computersystems, handheld devices, networking devices or any other device thatincorporates hard-wired and/or program logic to implement thetechniques.

For example, FIG. 23 is a block diagram that illustrates a computersystem 2300 upon which an embodiment of the invention may beimplemented. Computer system 2300 includes a bus 2302 or othercommunication mechanism for communicating information, and a processor2304 coupled with bus 2302 for processing information. Processor 2304may be, for example, a general purpose microprocessor.

Computer system 2300 also includes a main memory 2306, such as a randomaccess memory (RAM) or other dynamic storage device, coupled to bus 2302for storing information and instructions to be executed by processor2304. Main memory 2306 also may be used for storing temporary variablesor other intermediate information during execution of instructions to beexecuted by processor 2304. Such instructions, when stored innon-transitory storage media accessible to processor 2304, rendercomputer system 2300 into a special-purpose machine that is customizedto perform the operations specified in the instructions.

Computer system 2300 further includes a read only memory (ROM) 2308 orother static storage device coupled to bus 2302 for storing staticinformation and instructions for processor 2304. A storage device 2310,such as a magnetic disk or optical disk, is provided and coupled to bus2302 for storing information and instructions.

Computer system 2300 may be coupled via bus 2302 to a display 2312, suchas a computer monitor, for displaying information to a computer user. Aninput device 2314, including alphanumeric and other keys, is coupled tobus 2302 for communicating information and command selections toprocessor 2304. Another type of user input device is cursor control2316, such as a mouse, a trackball, or cursor direction keys forcommunicating direction information and command selections to processor2304 and for controlling cursor movement on display 2312. This inputdevice typically has two degrees of freedom in two axes, a first axis(e.g., x) and a second axis (e.g., y), that allows the device to specifypositions in a plane.

Computer system 2300 may implement the techniques described herein usingcustomized hard-wired logic, one or more ASICs or FPGAs, firmware and/orprogram logic which in combination with the computer system causes orprograms computer system 2300 to be a special-purpose machine. Accordingto one embodiment, the techniques herein are performed by computersystem 2300 in response to processor 2304 executing one or moresequences of one or more instructions contained in main memory 2306.Such instructions may be read into main memory 2306 from another storagemedium, such as storage device 2310. Execution of the sequences ofinstructions contained in main memory 2306 causes processor 2304 toperform the process steps described herein. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions.

The term “storage media” as used herein refers to any non-transitorymedia that store data and/or instructions that cause a machine tooperation in a specific fashion. Such storage media may comprisenon-volatile media and/or volatile media. Non-volatile media includes,for example, optical or magnetic disks, such as storage device 2310.Volatile media includes dynamic memory, such as main memory 2306. Commonforms of storage media include, for example, a floppy disk, a flexibledisk, hard disk, solid state drive, magnetic tape, or any other magneticdata storage medium, a CD-ROM, any other optical data storage medium,any physical medium with patterns of holes, a RAM, a PROM, an EPROM, aFLASH-EPROM, NVRAM, any other memory chip or cartridge.

Storage media is distinct from but may be used in conjunction withtransmission media. Transmission media participates in transferringinformation between storage media. For example, transmission mediaincludes coaxial cables, copper wire and fiber optics, including thewires that comprise bus 2302. Transmission media can also take the formof acoustic or light waves, such as those generated during radio-waveand infra-red data communications.

Various forms of media may be involved in carrying one or more sequencesof one or more instructions to processor 2304 for execution. Forexample, the instructions may initially be carried on a magnetic disk orsolid state drive of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over anetwork connection. A modem or network interface local to computersystem 2300 can receive the data. Bus 2302 carries the data to mainmemory 2306, from which processor 2304 retrieves and executes theinstructions. The instructions received by main memory 2306 mayoptionally be stored on storage device 2310 either before or afterexecution by processor 2304.

Computer system 2300 also includes a communication interface 2318coupled to bus 2302. Communication interface 2318 provides a two-waydata communication coupling to a network link 2320 that is connected toa local network 2322. For example, communication interface 2318 may bean integrated services digital network (ISDN) card, cable modem,satellite modem, or a modem to provide a data communication connectionto a corresponding type of telephone line. Wireless links may also beimplemented. In any such implementation, communication interface 2318sends and receives electrical, electromagnetic or optical signals thatcarry digital data streams representing various types of information.

Network link 2320 typically provides data communication through one ormore networks to other data devices. For example, network link 2320 mayprovide a connection through local network 2322 to a host computer 2324or to data equipment operated by an Internet Service Provider (ISP)2326. ISP 2326 in turn provides data communication services through theworld wide packet data communication network now commonly referred to asthe “Internet” 2328. Local network 2322 and Internet 2328 both useelectrical, electromagnetic or optical signals that carry digital datastreams. The signals through the various networks and the signals onnetwork link 2320 and through communication interface 2318, which carrythe digital data to and from computer system 2300, are example forms oftransmission media.

Computer system 2300 can send messages and receive data, includingprogram code, through the network(s), network link 2320 andcommunication interface 2318. In the Internet example, a server 2330might transmit a requested code for an application program throughInternet 2328, ISP 2326, local network 2322 and communication interface2318. The received code may be executed by processor 2304 as it isreceived, and/or stored in storage device 2310, or other non-volatilestorage for later execution.

Operations of processes described herein can be performed in anysuitable order unless otherwise indicated herein or otherwise clearlycontradicted by context. Processes described herein (or variationsand/or combinations thereof) may be performed under the control of oneor more computer systems configured with executable instructions and maybe implemented as code (e.g., executable instructions, one or morecomputer programs or one or more applications) executing collectively onone or more processors, by hardware or combinations thereof. The codemay be stored on a computer-readable storage medium, for example, in theform of a computer program comprising a plurality of instructionsexecutable by one or more processors. The computer-readable storagemedium may be non-transitory.

Conjunctive language, such as phrases of the form “at least one of A, B,and C,” or “at least one of A, B and C,” unless specifically statedotherwise or otherwise clearly contradicted by context, is otherwiseunderstood with the context as used in general to present that an item,term, etc., may be either A or B or C, or any nonempty subset of the setof A and B and C. For instance, in the illustrative example of a sethaving three members, the conjunctive phrases “at least one of A, B, andC” and “at least one of A, B and C” refer to any of the following sets:{A}, {B}, {C}, {A, B}, {A, C}, {B, C}, {A, B, C}. Thus, such conjunctivelanguage is not generally intended to imply that certain embodimentsrequire at least one of A, at least one of B and at least one of C eachto be present.

The use of any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate embodiments ofthe invention and does not pose a limitation on the scope of theinvention unless otherwise claimed. No language in the specificationshould be construed as indicating any non-claimed element as essentialto the practice of the invention.

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense. The sole and exclusive indicator of the scope of the invention,and what is intended by the applicants to be the scope of the invention,is the literal and equivalent scope of the set of claims that issue fromthis application, in the specific form in which such claims issue,including any subsequent correction.

Further embodiments can be envisioned to one of ordinary skill in theart after reading this disclosure. In other embodiments, combinations orsub-combinations of the above-disclosed invention can be advantageouslymade. The example arrangements of components are shown for purposes ofillustration and it should be understood that combinations, additions,re-arrangements, and the like are contemplated in alternativeembodiments of the present invention. Thus, while the invention has beendescribed with respect to exemplary embodiments, one skilled in the artwill recognize that numerous modifications are possible.

For example, the processes described herein may be implemented usinghardware components, software components, and/or any combinationthereof. The specification and drawings are, accordingly, to be regardedin an illustrative rather than a restrictive sense. It will, however, beevident that various modifications and changes may be made thereuntowithout departing from the broader spirit and scope of the invention asset forth in the claims and that the invention is intended to cover allmodifications and equivalents within the scope of the following claims.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

What is claimed is:
 1. A multiple-access base station having one or moretransceiver that handles communication with a plurality of terrestrialmobile stations, wherein a terrestrial mobile station, of the pluralityof terrestrial mobile stations, is configured to expect base stationcommunications with a terrestrial cellular base station that is (1)within a limited distance from the terrestrial mobile station and/or (2)moving less than a limited velocity relative to the terrestrial mobilestation, the multiple-access base station comprising: a data parser thatparses data received by the multiple-access base station according to aframe structure, wherein the frame structure defines which timeslots areallocated to which of the plurality of terrestrial mobile stations,wherein the frame structure comprises a plurality of slots each having azero or nonzero timeslot synchronization offset that provides forvariable transmission delays that are due to a distance from themultiple-access base station to the plurality of terrestrial mobilestations; a signal timing module that determines a signal timingadjustment relative to the frame structure for a transmitted signal tothe terrestrial mobile station based on a base-to-mobile distancebetween the multiple-access base station and the terrestrial mobilestation where the base-to-mobile distance exceeds the limited distance;and a programmable radio capable of communicating a communication fromthe multiple-access base station to the terrestrial mobile station usinga multiple-access protocol and taking into account the signal timingadjustment, such that the communication is compatible with, or appearsto the terrestrial mobile station to be, communication between aterrestrial cellular base station and the terrestrial mobile station,notwithstanding that the base-to-mobile distance exceeds the limiteddistance.
 2. The multiple-access base station of claim 1, furtheradapted to communicate with the plurality of terrestrial mobile stationswherein the plurality of terrestrial mobile stations comprises cellulartelephone handsets, smartphones, connected devices.
 3. Themultiple-access base station of claim 1, wherein the limited distance is120 kilometers and the base-to-mobile distance exceeds 120 kilometers.4. The multiple-access base station of claim 1, wherein themultiple-access protocol is an LTE protocol, the limited distance is 100kilometers, and the base-to-mobile distance exceeds 100 kilometers. 5.The multiple-access base station of claim 1, wherein the multiple-accessprotocol is an LTE-IoT protocol, the limited distance is 40 kilometers,and the base-to-mobile distance exceeds 40 kilometers.
 6. Themultiple-access base station of claim 1, wherein the multiple-accessprotocol is one of a CDMA-based protocol, an LTE protocol, a GSMprotocol, an OFDMA-based protocol, an FDMA-based protocol, a TDMA-basedprotocol, an EGPRS protocol, or an EDGE protocol.
 7. The multiple-accessbase station of claim 1, wherein the multiple-access base station is anorbital base station to be operated in Earth orbit.
 8. Themultiple-access base station of claim 7, wherein the limited distance is120 kilometers and base-to-mobile distances of terrestrial mobilestations of the plurality of terrestrial mobile stations are from about500 kilometers to about 750 kilometers.
 9. The multiple-access basestation of claim 1, wherein the multiple-access base station is a basestation operable in Earth atmosphere, including being mounted on or inone or more of an airplane, a drone, and/or a balloon.
 10. Themultiple-access base station of claim 9, wherein the limited distance is120 kilometers and the base-to-mobile distance exceeds 120 kilometers.11. The multiple-access base station of claim 1, further comprisingsignal allocation logic to allocate capacity of the multiple-access basestation to the plurality of terrestrial mobile stations, including theterrestrial mobile station, distributed over a plurality of timeslots, aplurality of carrier frequencies, a plurality of orthogonal subcarriersand/or a plurality of code sequences.
 12. The multiple-access basestation of claim 1, wherein the programmable radio is further capable oflistening for communications from the terrestrial mobile station using amultiple-access protocol, and the multiple-access base station furthercomprising: a range calculator that determines, for each terrestrialmobile station of the plurality of terrestrial mobile stations, itsbase-to-mobile distance, which is a distance from the multiple-accessbase station to the terrestrial mobile station; a receive timing modulethat determines timing of received signals of the terrestrial mobilestation relative to the frame structure based on the base-to-mobiledistance of the terrestrial mobile station; and an input signalallocator that allocates a listening timeslot in the frame structure tolisten for communications from the terrestrial mobile station where thelistening timeslot is timed based on the base-to-mobile distance of theterrestrial mobile station and the listening timeslot is one of aplurality of timeslots that are variably delayed in the frame structureto account for the multiple-access base station handling communicationsfrom the plurality of terrestrial mobile stations having a plurality ofbase-to-mobile distances.
 13. The multiple-access base station of claim12, wherein the plurality of timeslots are variably delayed in the framestructure to account for the plurality of terrestrial mobile stationshaving a plurality of base-to-mobile distances by assigning each of aplurality of different base-to-mobile distance ranges to each of aplurality of channel blocks.
 14. The multiple-access base station ofclaim 13, wherein the multiple-access base station is an orbital basestation to be operated in Earth orbit and wherein the plurality ofdifferent base-to-mobile distance ranges collectively cover a slantrange from a zenith distance through a minimum elevation distance,wherein the zenith distance is a distance between a zenith position of asatellite carrying the multiple-access base station relative to aterrestrial mobile station and wherein the minimum elevation distance isa distance between a position of the satellite when the terrestrialmobile station enters a design footprint of the satellite.
 15. Themultiple-access base station of claim 14, wherein the differentbase-to-mobile distance ranges each span approximately 34 to 35kilometers and a difference between the zenith distance and the minimumelevation distance is between 210 and 250 kilometers.
 16. Themultiple-access base station of claim 14, wherein a design footprint ofthe satellite is a circle, ellipse, rectangle and is independent of, ora function of an antenna and/or antenna beam shape.
 17. Amultiple-access base station having one or more transceiver that handlescommunication with a plurality of terrestrial mobile stations, wherein aterrestrial mobile station is configured to expect base stationcommunications with a terrestrial cellular base station that is (1)within a limited distance from the terrestrial mobile station and/or (2)moving less than a limited velocity relative to the terrestrial mobilestation, the multiple-access base station comprising: a data parser thatparses data received by the multiple-access base station according to aframe structure, wherein the frame structure defines which timeslots areallocated to which of the plurality of terrestrial mobile stations, andaccording to a multiple-access protocol in which the terrestrial mobilestation expects to receive signals at a specified frequency and totransmit signals at a specified frequency; a Doppler shift calculatorthat determines, for each terrestrial mobile station of the plurality ofterrestrial mobile stations, its Doppler shift due to velocity of itrelative to the multiple-access base station; a channel assignmentmodule that assigns each of the plurality of terrestrial mobile stationsto channel blocks in a plurality of channel blocks, wherein each achannel block has a terrestrial frequency and a Doppler frequencyoffset; a signal modulator that modulates signals to the terrestrialmobile station at the terrestrial frequency with the Doppler frequencyoffset, wherein the Doppler frequency offset at least approximatelycorresponds with an expected Doppler shift in signals transmitted to theterrestrial mobile station due to relative movement of themultiple-access base station and the terrestrial mobile station so thatthe terrestrial mobile station receives the signal at the terrestrialfrequency; and a programmable radio capable of receiving a communicationfrom the terrestrial mobile station using the multiple-access protocoland taking into account the Doppler frequency offset of the terrestrialmobile station, such that the communication is compatible with, orappears to the terrestrial mobile station to be, communication between aterrestrial cellular base station and the terrestrial mobile station,notwithstanding that the velocity of the terrestrial mobile stationrelative to the multiple-access base station exceeds the limitedvelocity.
 18. The multiple-access base station of claim 17, wherein thevelocity of the terrestrial mobile station relative to themultiple-access base station is a result of the multiple-access basestation being in Earth orbit, and wherein the Doppler frequency offsetvaries in 5 kilohertz increments.
 19. The multiple-access base stationof claim 17, further adapted to communicate with the plurality ofterrestrial mobile stations wherein the plurality of terrestrial mobilestations comprises cellular telephone handsets, smartphones, connecteddevices.
 20. The multiple-access base station of claim 17, wherein themultiple-access base station is an orbital base station to be operatedin Earth orbit.
 21. The multiple-access base station of claim 17,wherein the multiple-access base station is a base station operable inEarth atmosphere, including being mounted on or in one or more of anairplane, a drone, and/or a balloon.
 22. The multiple-access basestation of claim 17, further comprising signal allocation logic toallocate capacity of the multiple-access base station to the pluralityof terrestrial mobile stations, including the terrestrial mobilestation, distributed over a plurality of timeslots, a plurality ofcarrier frequencies, a plurality of orthogonal subcarriers and/or aplurality of code sequences.
 23. The multiple-access base station ofclaim 17, wherein each of the plurality of channel blocks has an uplinksubchannel and a downlink subchannel with a contiguous spectrum foruplink subchannels and a contiguous spectrum for downlink subchannels,and the channel blocks are assigned such that adjacent channel blocksare assigned to adjacent Doppler frequency offsets.
 24. Amultiple-access base station having one or more transceiver that handlescommunication with a plurality of terrestrial mobile stations, wherein aterrestrial mobile station is configured to expect base stationcommunications with a terrestrial cellular base station that is (1)within a limited distance from the terrestrial mobile station and/or (2)moving less than a limited velocity relative to the terrestrial mobilestation, the multiple-access base station comprising: a data parser thatparses data received by the multiple-access base station according to aframe structure, wherein the frame structure defines which timeslots areallocated to which of the plurality of terrestrial mobile stations,wherein the frame structure comprises a plurality of slots each having azero or nonzero timeslot synchronization offset that provides forvariable transmission delays that are due to a distance from themultiple-access base station to the plurality of terrestrial mobilestations and further according to a multiple-access protocol in whichthe terrestrial mobile station transmits at a expects to receive signalsat a specified frequency and to transmit signals at a terrestrialfrequency and is received with a Doppler frequency offset, and whereinthe multiple-access protocol specifies channel blocks in a plurality ofchannel blocks wherein each a channel block has a designated terrestrialfrequency and a designated timeslot; a signal timing module thatdetermines a signal timing adjustment relative to the frame structurefor a transmitted signal to the terrestrial mobile station based on abase-to-mobile distance between the multiple-access base station and theterrestrial mobile station where the base-to-mobile distance exceeds thelimited distance, wherein each channel block is assigned a designatedsignal timing adjustment; a Doppler shift calculator that determines,for each terrestrial mobile station of the plurality of terrestrialmobile stations, its Doppler shift due to velocity of it relative to themultiple-access base station and each channel block is assigned adesignated Doppler frequency offset; a dynamic channel allocator thatallocates each of the plurality of terrestrial mobile stations to adesignated channel block in the plurality of channel blocks based on itsdesignated signal timing adjustment and its designated Doppler frequencyoffset, with a number of channels in the designated channel blockcorresponding to a number of the plurality of terrestrial mobilestations that have, or are expected to have, a designated signal timingadjustment and designated Doppler frequency offset; a signal modulatorthat modulates signals to the terrestrial mobile station at theterrestrial frequency with the Doppler frequency offset, wherein theDoppler frequency offset at least approximately corresponds with anexpected Doppler shift in signals transmitted to the terrestrial mobilestation due to relative movement of the multiple-access base station andthe terrestrial mobile station so that the terrestrial mobile stationreceives the signal at the terrestrial frequency; and a programmableradio capable of receiving a communication from the terrestrial mobilestation using the multiple-access protocol and taking into account theDoppler frequency offset of the terrestrial mobile station, such thatthe communication is compatible with, or appears to the terrestrialmobile station to be, communication between a terrestrial cellular basestation and the terrestrial mobile station, notwithstanding that thebase-to-mobile distance exceeds the limited distance and notwithstandingthat the velocity of the terrestrial mobile station relative to themultiple-access base station exceeds the limited velocity.
 25. Themultiple-access base station of claim 24, wherein the velocity of theterrestrial mobile station relative to the multiple-access base stationis a result of the multiple-access base station being in Earth orbit,and wherein the Doppler frequency offset varies in 5 kilohertzincrements.
 26. The multiple-access base station of claim 24, furtheradapted to communicate with the plurality of terrestrial mobile stationswherein the plurality of terrestrial mobile stations comprises cellulartelephone handsets, smartphones, connected devices.
 27. Themultiple-access base station of claim 24, wherein the multiple-accessbase station is an orbital base station to be operated in Earth orbit.28. The multiple-access base station of claim 24, wherein themultiple-access base station is a base station operable in Earthatmosphere, including being mounted on or in one or more of an airplane,a drone, and/or a balloon.
 29. The multiple-access base station of claim24, further comprising signal allocation logic to allocate capacity ofthe multiple-access base station to the plurality of terrestrial mobilestations, including the terrestrial mobile station, distributed over aplurality of timeslots, a plurality of carrier frequencies, a pluralityof orthogonal subcarriers and/or a plurality of code sequences.